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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Hansen, Ed. 3 Internet-Draft AT&T Laboratories 4 Intended status: Informational L. Masinter 5 Expires: July 28, 2016 M. Hardy 6 Adobe 7 January 25, 2016 9 PDF for an RFC Series Output Document Format 10 draft-iab-rfc-use-of-pdf-00 12 Abstract 14 This document discusses options and requirements for the PDF 15 rendering of RFCs in the RFC Series, as outlined in RFC 6949. It 16 also discusses the use of PDF for Internet-Drafts, and available or 17 needed software tools for producing and working with PDF. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on July 28, 2016. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Choosing PDF versions and Standards . . . . . . . . . . . . . 3 55 3. Options and Requirements for PDF RFCs . . . . . . . . . . . . 4 56 3.1. "Visible" Requirements . . . . . . . . . . . . . . . . . 4 57 3.1.1. General Visible Requirements . . . . . . . . . . . . 4 58 3.1.2. Page Size, Margins . . . . . . . . . . . . . . . . . 5 59 3.1.3. Headers and Footers . . . . . . . . . . . . . . . . . 5 60 3.1.4. Paragraph Numbering . . . . . . . . . . . . . . . . . 5 61 3.1.5. Paged Content Layout . . . . . . . . . . . . . . . . 6 62 3.1.6. Typeface Choices . . . . . . . . . . . . . . . . . . 6 63 3.1.7. Hyphenation and Line Breaks . . . . . . . . . . . . . 7 64 3.1.8. Hyperlinks . . . . . . . . . . . . . . . . . . . . . 7 65 3.1.9. Similarity to Other Outputs . . . . . . . . . . . . . 8 66 3.2. "Invisible" Options and Requirements . . . . . . . . . . 9 67 3.2.1. Internal Text Representation . . . . . . . . . . . . 9 68 3.2.2. Unicode Support . . . . . . . . . . . . . . . . . . . 11 69 3.2.3. Image Processing (Artwork) . . . . . . . . . . . . . 11 70 3.2.4. Text Description of Images (Alt-Text) . . . . . . . . 11 71 3.2.5. Metadata Support . . . . . . . . . . . . . . . . . . 11 72 3.2.6. Document Structure Support . . . . . . . . . . . . . 12 73 3.2.7. Embedded Files . . . . . . . . . . . . . . . . . . . 12 74 3.3. Digital Signatures . . . . . . . . . . . . . . . . . . . 13 75 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 76 4.1. References . . . . . . . . . . . . . . . . . . . . . . . 13 77 4.2. Informative References . . . . . . . . . . . . . . . . . 14 78 Appendix A. History and Current Use of PDF with RFCs and 79 Internet-Drafts . . . . . . . . . . . . . . . . . . 15 80 A.1. RFCs . . . . . . . . . . . . . . . . . . . . . . . . . . 15 81 A.2. Internet-Drafts . . . . . . . . . . . . . . . . . . . . . 15 82 Appendix B. Paged Content Layout Quality . . . . . . . . . . . . 16 83 Appendix C. Tooling . . . . . . . . . . . . . . . . . . . . . . 16 84 C.1. PDF Viewers . . . . . . . . . . . . . . . . . . . . . . . 17 85 C.2. Printers . . . . . . . . . . . . . . . . . . . . . . . . 17 86 C.3. PDF Generation Libraries . . . . . . . . . . . . . . . . 17 87 C.4. Typefaces . . . . . . . . . . . . . . . . . . . . . . . . 18 88 C.5. Other Tools . . . . . . . . . . . . . . . . . . . . . . . 18 89 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 19 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 92 1. Introduction 94 The RFC Series is evolving, as outlined in [RFC6949]. Future 95 documents will use a canonical format, XML, with renderings in 96 various formats, including PDF. 98 Because PDF has a wide range of capabilities and alternatives, not 99 all PDFs are "equal". For example, visually similar documents could 100 consist of scanned or rasterized images, or include text layout 101 options, hyperlinks, embedded fonts, and digital signatures. (See 102 [I-D.hardy-pdf-mime] for a history of PDF.) 104 This document explains some of the relevant options and makes 105 recommendations, both for the RFC series and Internet-Drafts. 107 The PDF format and the tools to manipulate it are not as well known 108 as those for the other RFC formats, at least in the IETF community. 109 This document discusses some of the processes for creating and using 110 PDFs using both open source and commercial products. 112 The details described in this document are expected to change based 113 on experience gained in implementing the RFC production center's 114 toolset. Revised documents will be published capturing those changes 115 as the toolset is completed. Other implementers must not expect 116 those changes to remain backwards-compatible with the details 117 described in this document. 119 NOTE: [RFC-EDITOR: This note should be removed before publication.] 120 See for XML source, related 121 files, and an issue tracker for this document. 123 2. Choosing PDF versions and Standards 125 PDF [PDF] has gone through several revisions, primarily for the 126 addition of features. PDF features have generally been added in a 127 way that older viewers 'fail gracefully', but even so, the older the 128 PDF version produced, the more legacy viewers will support that 129 version, but the fewer features will be enabled. 131 As PDF has evolved a broad set of capabilities, additional standards 132 for PDF files are applicable. These standards establish ground rules 133 that are important for specific applications. For example PDF/X was 134 specifically designed for Prepress digital data exchange, with 135 careful attention to color management and printing instructions. The 136 PDF/E standard was designed for engineering documents with dynamic 137 workflows (where a document continues to be revised after 138 publication) and allows interactive media (including animation and 139 3D). 141 Two additional standards families are important to the RFC format, 142 though: long-term preservation (PDF/A), and user accessibility (PDF/ 143 UA [PDFUA]). These then have sub-profiles (PDF/A-1, PDF/A-2 [PDFA2], 144 PDF/A-3 [PDFA3]), each of which have conformance levels. These 145 standards are then supported by various software libraries and tools. 147 It is effective and useful to use these standards to capture PDF for 148 RFC requirements, and they will make the PDF files useful in 149 workflows that expect them. 151 Recommendations: 153 Use PDF 1.7; although relatively recent, it is well supported by 154 widely available viewers. 156 For RFCs, require PDF/A-3 with conformance level "U". This 157 captures the archivability and long-term stability of PDF 1.7 158 files, mandatory Unicode mapping, and many of the requirement 159 features. 161 Use PDF/A-3 for embedding additional data (including the XML 162 source file) in RFCs and Internet-Drafts. 164 Use PDF/UA for user accessibility. 166 3. Options and Requirements for PDF RFCs 168 This section lays out options and requirements for PDFs produced by 169 the RFC editor for RFCs. There are two sections: "Visible" options 170 are related to how the PDF appears when it is viewed with a PDF 171 viewer. "Internal Structure" options affect the ability to process 172 PDFs in other ways, but do not control the way the document appears. 173 (Of course, a viewer UI might display processing capabilities, such 174 as showing whether a document has been digitally signed.) 176 In many cases, the choice of PDF requirements is heavily influenced 177 by the capabilities of available tools to create PDFs. Most of the 178 discussion of tooling is to be found in Appendix C. 180 3.1. "Visible" Requirements 182 PDF supports rich visible layout of fixed-sized pages. 184 3.1.1. General Visible Requirements 186 For a consistent "look" of RFC and good style, the PDFs produced by 187 the RFC editor should have a clear, consistent, identifiable and 188 easy-to-read style. They should print well on the widest range of 189 printers, and look good on displays of varying resolution. 191 3.1.2. Page Size, Margins 193 PDF files are laid out for a particular size of page and margins. 194 There are two paper sizes in common use: "US Letter" (8.5 x 11 195 inches, 216x279 mm, in popular use in North America) and "A4" 196 (210x297 mm, 8.27x11.7 inches, standard for the rest of the world). 197 Usually PDF printing software is used in a "shrink to fit" mode where 198 the printing is adjusted to fit the paper in the printer. There is 199 some controversy, but the argument that A4 is an international 200 standard is compelling. However, if the margins and header 201 positioning are chosen appropriately, the document can be printed 202 without any scaling. 204 Recommendation: The Internet-Draft and RFC processors should produce 205 A4 size by default. However, the margins and header positioning need 206 to be chosen to look good on both paper sizes without scaling. 208 3.1.3. Headers and Footers 210 Page headers and footers are part of the page layout. There are a 211 variety of options. Note that page headers and footers in PDF can be 212 typeset in a way that the entire (longer) title might fit. 214 Recommendation: Page headers and footers should contain similar 215 information as the headings in the current text versions of 216 documents, including page numbers, title, author, working group. 217 However, the page headers and footers should be typeset in a way so 218 as to be unobtrusive. The page headers and footers should be placed 219 into the PDF in a way not to interfere with screen readers. 221 3.1.4. Paragraph Numbering 223 One common feature of the Internet-draft output formats are optional 224 visible paragraph numbers, to aid in discussions. In the PDF and 225 thus printed rendition, it is possible to make paragraph numbers 226 unobtrusive, and even to impinge on the margins. 228 Recommendation: When the XML "editing=yes" option has been chosen, 229 show paragraph numbers in the right margin, typeset in a way so as to 230 be unobtrusive. (The right margin instead of the left margin 231 prevents the paragraph numbers from being confused with the section 232 numbers.) If possible, the paragraph numbers should be coded in a 233 way that they do not interfere with screen readers. 235 3.1.5. Paged Content Layout 237 By its nature, PDF is paginated, so pagination issues must be 238 considered. This is reflected in two areas: running headers and 239 footers, and how text is layed out on a page for optimal reading. 241 Appendix B describes the process of creating a paged document from 242 running text such that related material is present on the same page 243 together and artifacts of pagination don't interfere with easy 244 reading of the document. 246 Layout engines differ in the quality of the algorithms used to 247 automate these processes. In some cases, the automated processes 248 require some manual assistance to ensure, for example, that a text 249 line intended as a heading is "kept" with the text it is heading for. 251 Recommendations: 253 o Headers and footers should be printed on each page. The 254 information should include the RFC number or internet-draft name, 255 the page number, the category (informational, etc.), a shortened 256 version of the authors' names, the date of the RFC or internet- 257 draft, and the short form of the document title. 259 o Choose a layout engine so that manual intervention is minimized, 260 and that widow and orphan processing, heading and title 261 contiguation are automatic. 263 3.1.6. Typeface Choices 265 A PDF may refer to a font by name, or it may use an embedded font. 266 When a font is not embedded, a PDF viewer will attempt to locate a 267 locally installed font of the same name. If it can not find an exact 268 match, it will find a "close match". If a close match is not 269 available, it will fall back to something implementation dependent 270 and usually undesirable. 272 In addition, the PDF/A standards mandate the embedding of fonts. 273 Instead of using additional software to embed the fonts, the software 274 generating the PDF files should produce PDF/A-conforming files 275 directly, thus ensuring that all glyphs include Unicode mappings and 276 embedded fonts from the outset. 278 If the HTML version of the document is being visually mimicked, the 279 font(s) chosen should have both variable width and constant width 280 components, as well as bold and italic representations. 282 The typefaces used by Internet-Drafts and by RFCs need not be 283 identical. 285 Few fonts have glyphs for the entire repertoire of Unicode 286 characters; for this purpose, the PDF generation tool may need a set 287 of fonts and a way of choosing them. The RFC Editor is defining 288 where Unicode characters may be used within 289 RFCs.[I-D.flanagan-nonascii] 291 Typefaces are typically licensed and, in many cases, there is a fee 292 for use by PDF creation tools; however, not for display or print of 293 the embedded fonts. 295 Recommendations: 297 o For consistent viewing, all fonts should be embedded. The fonts 298 used must be available for use by the IETF community. Some 299 discussion of available typefaces can be found in Appendix C.4. 301 o The choice of type faces with respect to serif, sans serif, 302 monospace, etc., should follow the recommendations for HTML and 303 CSS rendering [I-D.hildebrand-html-rfc] and 304 [I-D.flanagan-rfc-css]. 306 o The range of Unicode characters allowed in the XML source for 307 Internet-Drafts and RFCs may be bounded by the availability of 308 embeddable fonts with appropriate glyphs [I-D.flanagan-nonascii]. 310 3.1.7. Hyphenation and Line Breaks 312 Typically, when doing page layout of running text, especially with 313 narrow page width and long words, layout processors of English text 314 often have the option of hyphenating words, or using existing hyphens 315 as a place to introduce word breaks. However, line breaks inserted 316 mid-word where the "word" is actually technically a sequence of 317 characters representing a protocol element or protocol sequence is 318 actively harmful. 320 Recommendation: avoid introducing hyphenated line breaks mid-word 321 into the visual display, consistent with requirements for plain text 322 and HTML. 324 3.1.8. Hyperlinks 326 PDF supports hyperlinks both to sections of the same document and to 327 other documents. 329 The conversion to PDF can generate: 331 o hyperlinks within the document 333 o hyperlinks to other RFCs and Internet-Drafts 335 o hyperlinks to external locations 337 o hyperlinks within a table of contents 339 o hyperlinks within an index 341 Recommendations: 343 o All hyperlinks available in the HTML rendition of the RFC should 344 also be visible and active in the PDF produced. This includes 345 both internal hyperlinks and hyperlinks to external resources. 347 o The table of contents, including page numbers, are useful when 348 printed. These should also be hyperlinked to their respective 349 sections. 351 o As specified in the section on Referencing RFCs in [RFC7322], 352 hyperlinks to RFCs from the references section should point to the 353 RFC "info" page, which then links to the various formats 354 available. 356 o Hyperlinks to Internet-Drafts from the references section should 357 point to the datatracker entry page for the draft, which then 358 links to the various formats available. 360 3.1.9. Similarity to Other Outputs 362 There is some advantage to having the PDF files look like the text or 363 HTML renderings of the same document. There are several options even 364 so. The PDF 366 1. could look like the text version of the document, or 368 2. could look like the text version of the document but with 369 pictures rendered as pictures instead of using their ASCII-art 370 equivalent, or 372 3. could look like the HTML version. 374 Recommendation: the PDF rendition should look like the HTML 375 rendition, at least in spirit. Some differences from the HTML 376 rendition would include different typeface and size (chosen for 377 printing), page numbers in the table of contents and index, and the 378 use of page headers and footers. 380 Most of the choices used for the [I-D.hildebrand-html-rfc] rendering 381 and [I-D.flanagan-rfc-css] are thus applicable. See those documents 382 for specifics on the rendering of the specific XML elements. Some 383 notes are: 385 Every place in the document that would receive an HTML ID would be 386 given an identical PDF named destination. In addition, a named 387 destination will be created for each page with the form "pg-#", as 388 in "pg-35". 390 No pilcrows are generated or made visible. 392 The table of contents (generated if the XML's element's 393 tocInclude attribute has the value "true") will have the section 394 number linked to that section named destination, but will also 395 include a page number that is linked to the page named 396 destination. The section title and the page number will be 397 separated by a visually-appropriate separator and the page numbers 398 will be aligned with each other. 400 The index (generated if the XML's element's indexInclude 401 attribute has the value "true") will have the section number 402 linked to that section named destination, but will also include a 403 page number that is linked to the page named destination. 405 The running header in one line (on page 2 and all subsequent 406 pages) has the RFC number on the left (RFC NNNN), the (possibly 407 shortened form) title centered, and the date (Month Year) on the 408 right. The text is rendered in a way that is visually 409 unobtrusive. 411 The running footer in one line (on all pages) has the author's 412 last name on the left, category centered, and the page number on 413 the right ([Page N]). The text is rendered in a way that is 414 visually unobtrusive. 416 3.2. "Invisible" Options and Requirements 418 PDF offers a number of features which improve the utility of PDF 419 files in a variety of workflows, at the cost of extra effort in the 420 xml2rfc conversion process; the tradeoffs may be different for the 421 RFC editor production of RFCs and for Internet-Drafts. 423 3.2.1. Internal Text Representation 425 The contents of a PDF file can be represented in many ways. The PDF 426 file could be generated: 428 o as an image of the visual representation, such as a JPEG image of 429 the word "IETF". That is, there might be no internal 430 representation of letters, words or paragraphs at all. 432 o placing individual characters in position on the page, such as 433 saying "put an 'F' here", then "put an 'T' before it", then "put 434 an 'E' before that", then "put an 'I' before that" to render the 435 word "IETF". That is, there might be no internal representation 436 of words or paragraphs at all. 438 o placing words in position on the page, such as keeping the word 439 "IETF" would be kept together. That is, there might be no 440 internal representation of paragraphs at all. 442 o ensuring that the running order of text in the content stream 443 matches the logical reading order. That is, a sentence such as 444 'The Internet Engineering Task Force (IETF) supports the 445 Internet.' would be kept together as a sentence, and multiple 446 sentences within a paragraph would be kept together. 448 All of these end up with essentially the same visual representation 449 of the output. However, each level has tradeoffs for auxiliary uses, 450 such as searching or indexing, commenting and annotation, and 451 accessibility (text-to-speech). Keeping the running order of text in 452 the content stream in the proper order supports all of these 453 auxiliary uses. 455 In addition, the "role map" feature of PDF 456 () would additionally 458 allow for the mapping of the logical tags found in the original XML 459 into tags in the PDF. 461 Recommendations: 463 o Text in content streams should follow the XML document's logical 464 order (in the order of tags) to the extent possible. This will 465 provide optimal reuse by software that does not understand Tagged 466 PDF. (PDF/UA requires this.) 468 o It might be possible to use the "role map" annotation to capture 469 enough of the xml2rfc source structure, to the point where it is 470 possible to reconstruct the XML source structure completely. 471 However, there is not a compelling case to do so over embedding 472 the original XML, as described in Section 3.2.7. 474 3.2.2. Unicode Support 476 PDF itself does not require use of Unicode. Text is represented as a 477 sequence of glyphs which then can be mapped to Unicode. 479 Recommendations: 481 PDF files generated must have the full text, as it appears in the 482 original XML. 484 Unicode normalization may occur. 486 Text within SVG for SVG images should also have Unicode mappings. 488 Alt-text for images should also support Unicode. 490 3.2.3. Image Processing (Artwork) 492 The XML allows both ASCII art and SVG to be used for artwork. 494 Recommendations: 496 If both ASCII art and SVG are available for a picture, the SVG 497 artwork should be the preferred over the ASCII artwork. 499 ASCII artwork must be rendered using a monospace font. 501 3.2.4. Text Description of Images (Alt-Text) 503 Guidelines for accessibility of PDF recommend that images, formulas, and other non-text 505 items provide textual alternatives, using the '/Alt' Tag in PDF to 506 provide human-readable text that can be vocalized by text-to-speech 507 technology. 509 Recommendation: Any alt-text for artwork and figures available in the 510 XML source should be stored using the PDF /Alt property. Internet 511 draft authors and the RFC editor should ensure inclusion of alt-text 512 for all SVG or images, within the XML source. 514 3.2.5. Metadata Support 516 Metadata encodes information about the document authors, the document 517 series, date created, etc. Having this metadata within the PDF file 518 allows it to be used by search engines, viewers and other reuse 519 tools. PDF supports embedded metadata in a variety of ways, 520 including using XMP [XMP], the Extensible Metadata Platform (XMP). 521 The RFC editor maintains metadata about an RFC on its info page. 523 Recommendation: The PDFs generated should have all of the metadata 524 from the XML version embedded directly as XMP metadata, including the 525 author, date, the document series, and a URL for where the document 526 can be retrieved. This information should be consistent with the RFC 527 editor info page at the time of publication. 529 3.2.6. Document Structure Support 531 PDF supports an "outline" feature where sections of the document are 532 marked; this could be used in addition to the table of contents as a 533 navigation aid. 535 The section structure of an RFC can be mapped into the PDF elements 536 for the document structure. This will allow the bookmark feature of 537 PDF readers to be used to quickly access sections of the document. 539 Recommendation: The section structure of an RFC should be mapped into 540 the PDF elements for the document structure. This would include 541 section headings for the boilerplate sections such as the Abstract, 542 Status of the Document, Table of Contents, and Author Addresses, plus 543 the obvious section headings that are normally included in the 544 Table of Contents. If possible, this should be done in a way that 545 the same fragment identifiers for the HTML version of the RFC will 546 work for the PDF version. 548 3.2.7. Embedded Files 550 PDF has the capability of including other files; the files may be 551 labeled both by a media type and a role, the AFRelationship key 552 [PDFA3]. In this way, the PDF file acts also as a container. 554 Embedded content may be compressed. 556 Many PDF viewers support the ability to view and extract embedded 557 files, although this capability is not universal. 559 Embedding content in the PDF file allows the PDF to act as a complete 560 package, which can be transformed, archived, and digitally signed. 561 (Some sample code illustrating how items can be attached to a PDF 562 file and subsequently extracted can be found at 563 .) Useful possibilities: 565 Embed the source XML input file itself within the PDF. If the 566 source SVG and images for illustrations are also embedded, this 567 would make the PDF file totally self-referential. 569 Embed directly extractable components that are useful for 570 independent processing, including ABNF, MIBs, source code for 571 reference implementations. This capability might be supported 572 through other mechanisms from the XML source files, but could also 573 be supported within the PDF. 575 Finding, extracting and embedding other components may require 576 additional markup to clearly identify them, and additional review 577 to ensure the correctness of embedded files that are not visible. 579 Recommendations: 581 Embed the XML source and all illustrations, for RFCs, as a 582 standard feature for xml2rfc's PDF output. 584 If possible, make this a standard feature for Internet-Drafts as 585 well. 587 Named entries should be embedded. 589 Bitmap images (SVG sources, JPEGs, PNGs, etc) should be embedded. 591 3.3. Digital Signatures 593 PDF has supported digital signatures since PDF 1.2. There are 594 multiple methods for signing PDF files. The signature is intended to 595 apply not only to the bits in the file (that they haven't been 596 modified) but also to lock down the visual presentation as well. 598 The RFC Editor and staff are at times called to provide evidence that 599 a particular RFC is the "original" and has not been visually 600 modified, and there may be other use cases. As signatures also apply 601 to embedded content, embedding the XML source will provide a way of 602 signing the source XML as well. 604 Recommendation: PDFs produced by the RFC editor should be signed with 605 a PDF digital signature. The management of certificates for the RFC 606 editor function needs further review. 608 Recommendation: At this time, the authors see no need for Internet- 609 Drafts to be signed with a PDF digital signature. 611 4. References 613 4.1. References 615 [PDF] ISO, "Portable document format -- Part 1: PDF 1.7", 616 ISO 32000-1, 2008. 618 Also available free from Adobe. 620 [XMP] ISO, "Extensible metadata platform (XMP) specification -- 621 Part 1: Data model, serialization and core properties", 622 ISO 16684-1, 2012. 624 Not available free, but there are a number of descriptive 625 resources, e.g., 628 [PDFA2] ISO, "Electronic document file format for long-term 629 preservation -- Part 2: Use of ISO 32000-1 (PDF/A-2).", 630 ISO 19005-2, 2011. 632 [PDFA3] ISO, "Electronic document file format for long-term 633 preservation -- Part 3: Use of ISO 32000-1 with support 634 for embedded files (PDF/A-3)", ISO 19005-3, 2012. 636 [PDFUA] ISO, "Electronic document file format enhancement for 637 accessibility -- Part 1: Use of ISO 32000-1 (PDF/UA-1)", 638 ISO 19005-3, 2012. 640 4.2. Informative References 642 [RFC6949] Flanagan, H. and N. Brownlee, "RFC Series Format 643 Requirements and Future Development", RFC 6949, 644 DOI 10.17487/RFC6949, May 2013, 645 . 647 [RFC7322] Flanagan, H. and S. Ginoza, "RFC Style Guide", RFC 7322, 648 DOI 10.17487/RFC7322, September 2014, 649 . 651 [I-D.flanagan-nonascii] 652 Flanagan, H., "The Use of Non-ASCII Characters in RFCs", 653 draft-flanagan-nonascii-06 (work in progress), November 654 2015. 656 [I-D.flanagan-rfc-css] 657 Flanagan, H., "CSS Requirements for RFCs", draft-flanagan- 658 rfc-css-04 (work in progress), September 2015. 660 [I-D.hildebrand-html-rfc] 661 Hildebrand, J. and P. Hoffman, "HyperText Markup Language 662 Request For Comments Format", draft-hildebrand-html-rfc-10 663 (work in progress), August 2015. 665 [I-D.hardy-pdf-mime] 666 Hardy, M., Masinter, L., and D. Johnson, "The application/ 667 pdf Media Type", draft-hardy-pdf-mime-00 (work in 668 progress), July 2014. 670 4.3. URIs 672 [1] https://sourceforge.net/projects/ 673 sourcesans.adobe/?source=directory 675 [2] https://sourceforge.net/projects/ 676 sourceserifpro.adobe/?source=directory 678 [3] https://sourceforge.net/projects/ 679 sourcecodepro.adobe/?source=drectory 681 [4] https://www.rosettatype.com/Skolar 683 [5] https://www.google.com/get/noto/ 685 Appendix A. History and Current Use of PDF with RFCs and Internet- 686 Drafts 688 NOTE: this section is meant as an overview to give some background. 690 A.1. RFCs 692 The RFC series has for a long time accepted Postscript renderings of 693 RFCs, either in addition to or instead of the text renderings of 694 those same RFCs. These have usually been produced when there was a 695 complicated figure or mathematics within the document. For example, 696 consider the figures and mathematics found in RFC 1119 and RFC 1142, 697 and compare the figures found in the text version of RFC 3550 with 698 those in the Postscript version. The RFC editor has provided a PDF 699 rendering of RFCs. Usually, this has been a print of the text file 700 that does not take advantage of any of the broader PDF functionality, 701 unless there was a Postscript version of the RFC, which would then be 702 used by the RFC editor to generate the PDF. 704 A.2. Internet-Drafts 706 In addition to PDFs generated and published by the RFC editor, the 707 IETF tools community has also long supported PDF for Internet-Drafts. 708 Most RFCs start with Internet-Drafts, edited by individual authors. 709 The Internet-Drafts submission tool at https://datatracker.ietf.org/ 710 submit/ accepts PDF and Postscript files in addition to the 711 (required) text submission and (currently optional) XML. If a PDF 712 wasn't submitted for a particular version of an Internet-Draft, the 713 tools would generate one from the Postscript, HTML, or text. 715 Appendix B. Paged Content Layout Quality 717 The process of creating a paged document from running text typically 718 involves ensuring that related material is present on the same page 719 together, and that artifacts of pagination don't interfere with easy 720 reading of the document. Typical high-quality layout processors do 721 several things: 723 Widow and Orphan Management: Widows and orphans 724 () should be 725 avoided automatically (unless the entire paragraph is only one 726 line). Ensure that a page break does not occur after the first 727 line of a paragraph (orphans), if necessary, using slightly longer 728 page sizes. Similarly, ensure that a page break does not occur 729 before the last line of a paragraph (widows). 731 Keep Section Heading Contiguous: Do not insert a page break 732 immediately after a section heading. If there isn't room on a 733 page for the first (two) lines of a section after the section 734 heading, insert a page break before the heading. 736 Avoid Splitting Artwork: Figures should not be split from figure 737 titles. If possible, keep the figure on the same page as the 738 (first) mention of the figure. 740 Headers for Long Tables after Page Breaks: Another common option in 741 producing paginated documents is to include the column headings of 742 a table if the table cannot be displayed on a single page. 743 Similarly, tables should not be split from the table titles. 745 keepWithNext and keepWithPrevious: The XML attributes of 746 "keepWithNext" and "keepWithPrevious" should be followed whenever 747 possible. 749 Whitespace Preservation: The XML entities such as NBSP and NBHYPHEN 750 should be followed as directed whenever possible. 752 Appendix C. Tooling 754 This section discusses tools for viewing, comparing, creating, 755 manipulating, transforming PDF files, including those currently in 756 use by the RFC editor and Internet-Drafts, as well as outlining 757 available PDF tools for various processes. 759 C.1. PDF Viewers 761 As with most file formats, PDF files are experienced through a reader 762 or viewer of PDF files, and there are numerous viewers. One partial 763 list of PDF viewers can be found at . 766 PDF viewers vary in capabilities, and it is important to note which 767 PDF viewers support the features utilized in PDF RFCs and Internet- 768 Drafts (features such as links, digital signatures, Tagged PDF and 769 others mentioned in Section 3). 771 A survey of the IETF community might broaden the list of viewers in 772 common use, but an initial list to consider include some that are 773 currently maintained and supported viewers and legacy systems. 774 Maintained viewers include: 776 Adobe Reader Multiple platforms. Supports all of the features on 777 most platforms. 779 Google Chrome Multiple platforms. Web browser which includes PDF 780 support. Rapidly moving target, open source. 782 PDF.js Multiple platforms. A JavaScript library to convert PDF 783 files into HTML5, usable as a web-based viewer that can be 784 included in web browsers. Used by Mozilla Firefox. Also rapidly 785 moving target. 787 Foxit Reader Multiple platforms. PDF Viewer / Reader for Desktop 788 computer and Mobile Devices. Recently licensed by Google, and the 789 code for this purpose was made open source; see . 793 Several "legacy" viewers to consider include: Ghostview, Xpdf. 795 C.2. Printers 797 While almost all viewers also support printing of PDF files, printing 798 is one of the most important use cases for PDFs. Some printers have 799 direct PDF support. 801 C.3. PDF Generation Libraries 803 Because the xml2rfc format is a unique format, software for 804 converting XML source documents to the various formats will be 805 needed, including PDF generation. 807 One promising direction is suggested in 808 : using XSLT to generate XSL-FO which 810 is then processed by a formatting object processor such as Apache 811 FOP. 813 Several libraries are also available for generating PDF signatures. 815 C.4. Typefaces 817 This section is intended to discuss available typefaces that might 818 satisfy requirements. Some openly available fixed-width typefaces 819 (without extensive Unicode support, however) include: 821 o Source Sans [1] 823 o Source Serif Pro [2] 825 o Source Code Pro [3] 827 A font that looks promising for its broad Unicode support is Skolar 828 [4], but it requires licensing. Another potentially useful set of 829 typefaces is the Noto [5] family from Google. 831 C.5. Other Tools 833 In addition to generating and viewing PDF, other categories of PDF 834 tools are available and may be useful both during specification 835 development and for published RFCs. These include tools for 836 comparing two PDFs, checkers that could be used to validate the 837 results of conversion, reviewing and commentary tools that attach 838 annotations to PDF files, and digital signature creation and 839 validation. 841 Validation of an arbitrary author-generated PDF file would be quite 842 difficult; there are few PDF validation tools. However, if RFCs and 843 Internet-Drafts are generated by conversion from XML via xml2rfc, 844 then explicit validation of PDF and adherence to expected profiles 845 would mainly be useful to ensure that xml2rfc has functioned 846 properly. 848 Recommendations: 850 o Discourage (but allow) submission of a PDF representation for 851 Internet-Drafts. In most cases, the PDF for an Internet-Draft 852 should be produced automatically when XML is submitted, with an 853 opportunity to verify the conversion. 855 Appendix D. Acknowledgements 857 The input of the following people is gratefully acknowledged: Nevil 858 Brownlee (ISE), Brian Carpenter, Chris Dearlove, Martin Duerst, 859 Heather Flanagan (RSE), Joe Hildebrand, Paul Hoffman, Duff Johnson, 860 Ted Lemon, Henrik Levkowetz, Julian Reschke, Adam Roach, Leonard 861 Rosenthol, Alice Russo, Robert Sparks, Andrew Sullivan, and Dave 862 Thaler. 864 Authors' Addresses 866 Tony Hansen (editor) 867 AT&T Laboratories 868 200 Laurel Ave. South 869 Middletown, NJ 07748 870 USA 872 Email: tony@att.com 874 Larry Masinter 875 Adobe 876 345 Park Ave 877 San Jose, CA 95110 878 USA 880 Email: masinter@adobe.com 881 URI: http://larry.masinter.net 883 Matthew Hardy 884 Adobe 885 345 Park Ave 886 San Jose, CA 95110 887 USA 889 Email: mahardy@adobe.com