[css-page] Additional Standard Paper Keywords for (page-)size

This is a consolidated and updated revision of #328 from mid-2016.
When @fantasai closed that issue by editor discretion, she said:

I agree with [@frivoal] that unless there is specific demand for certain keywords,
we should not add them pre-emptively.

I shall show that there is specific demand for certain keywords, in the fist section below.

Moreover, although not recorded explicitly and lacking a WG decision, there appears to have been somewhat of a consensus back then that keywords should be added to CSS for
commonly used sizes with
standardized identifiers and
hard to remember dimensions.
I shall document those as well, in the second section below.

Interoperability for International Sheet and Envelope Sizes

TL;DR: Add all missing keywords for standard paper sizes in the ISO 216 A and B series, the ISO 269 C series and the JIS P 0138 B series:

• A0, A1, A2 and A6, A7, A8, A9, A10
• B0, B1, B2, B3 and B6, B7, B8, B9, B10
• JIS-B0, JIS-B1, JIS-B2, JIS-B3 and JIS-B6, JIS-B7, JIS-B8, JIS-B9, JIS-B10
• C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10

While web browser developers may seem less than keen to invest more resources in css-page than absolutely necessary, there are several applications specializing in CSS-driven PDF creation which strongly rely on this particular Module and may wish to extend its capabilities. The W3C should care about harmonizing their use of CSS to ease interchange and thereby making manuscripts more universal.

WeasyPrint and Vivliostyle support all currently standardized keywords for size (or page-size in the future) standardized by CSS in level 3: A3, A4, A5, B4, B5, JIS-B4, JIS-B5 (and American Letter, Legal, Ledger). Their open source code shows that it would be ridiculously simple to add more named sizes.
wkhtmltopdf uses plain headless Qt Webkit and relies on its capabilities.
Addendum: paged.js seems to add all of the A series (although A8 and A9 are undocumented).

Existing implementations from PDF Reactor, Prince and Antenna House support more than those specified keywords, but they use partially incompatible custom keywords for the same physical sizes. In one case, there are three different custom keywords for the same size: ANSI-C, C and Broadsheet for 17in 22in. This hinders stylesheet interchange – avoiding this is prime motivation for standardization.

However, at least two existing implementations agree on keywords and definitions of all ISO 216 formats.
Since ISO paper sizes result from an irrational aspect ratio of √2:1 and an integer base area, A(A0) = 1 m², their odd edge lengths are hard to remember exactly.
Their popularity, stability, ease of implementation and the difficulty of using their numeric values, makes them ideal candidates to add.

In the following table, the custom keywords already supported by implementations are highlighted if they are identical to the proposed keyword. In particular, the ISO- prefix supported by Antenna House in aliases shall not be adopted.

Proposal	Size	CSS	Prince, PDF Reactor	Antenna House
A10	26mm 37mm	—	A10	—
C10	28mm 40mm	—	C10	—
B10	31mm 44mm	—	B10	—
A9	37mm 52mm	—	A9	—
C9	40mm 57mm	—	C9	—
B9	44mm 62mm	—	B9	—
A8	52mm 74mm	—	A8	—
C8	57mm 81mm	—	C8	—
B8	62mm 88mm	—	B8	—
A7	74mm 105mm	—	A7	—
C7	81mm 114mm	—	C7	—
B7	88mm 125mm	—	B7	—
A6	105mm 148mm	—	A6	A6
C6	114mm 162mm	—	C6	ISO-C6
B6	125mm 176mm	—	B6	ISO-B6, B6
A5	148mm 210mm	A5	A5	A5
C5	162mm 229mm	—	C5	ISO-C5
B5	176mm 250mm	B5	B5	ISO-B5, B5
A4	210mm 297mm	A4	A4	A4
C4	229mm 324mm	—	C4	ISO-C4
B4	250mm 353mm	B4	B4	ISO-B4, B4
A3	297mm 420mm	A3	A3	A3
C3	324mm 458mm	—	C3	ISO-C3
B3	353mm 500mm	—	B3	—
A2	420mm 594mm	—	A2	—
C2	458mm 648mm	—	C2	—
B2	500mm 707mm	—	B2	—
A1	594mm 841mm	—	A1	—
C1	648mm 917mm	—	C1	—
B1	707mm 1000mm	—	B1	—
A0	841mm 1189mm	—	A0	—
C0	917mm 1297mm	—	C0	—
B0	1000mm 1414mm	—	B0	—

Usability for common, standardized, odd-valued Page Sizes

TL;DR: Optionally, add keywords for the standard paper sizes in ISO 217 (raw oversizes) and ISO 5457 (untrimmed drawing paper sizes).

If the interoperability argument in the first section above was not convincing enough to add keywords for the missing sizes from ISO 216 and all of ISO 269, they should also qualify due to having standardized identifiers and odd length values, and even if some were not commonly used, it would be beneficial to add the complete series nevertheless, for consistency, so authors do not have to remember which sizes do not have a keyword in CSS.

The international standard paper sizes – series A and B defined in ISO 216 and series C in ISO 269, which has been withdrawn in 2009 but still exists in local norms like DIN 476-2 – have been adopted by many national standardization bodies.
Some have extended definitions for special purposes, e.g. the RA and SRA series from ISO 217, German 2A0 from DIN 476 or the now-withdrawn Swedish D–G series from SIS 014711 and, of course, the Japanese B series from JIS P 0138 that is already recognized partially by CSS.
For envelopes in particular, there are also some sizes with an 2:1 aspect ratio that combine the non-common edges of two adjacent sizes, e.g. C5/C4.
The respective Wikipedia article for paper size is quite comprehensive.

However, most of these sizes are of limited interest to most CSS authors, at least with consumer printers, but those who need any of them would certainly welcome their addition to the standard.

Since CSS introduced the JIS- prefix to distinguish Japanese B sizes from international ones defined by ISO, it is not surprising that ISO-, US- and ANSI- also appear as prefixes for short size codes in existing implementations.

Proposed side rule:

All (new) page size keywords that use an alphanumeric code instead of a proper name, shall employ a prefix for the (original) issuing standardization body, e.g. JIS-, DIN-, SIS-, GOST-, BS-, ANSI-, ASME-, unless the code has been adopted by ISO (even if it has been deprecated since).

I do not propose any of those local sizes here, although some are apparently used frequently.
The only local sizes I am proposing are the rest of the JIS P 0138 series. Keywords for B4 and B5 are already specified and an analogous one for B6 is already supported in at least one implementation.

Proposal	Size	CSS	Antenna House
JIS-B12	16mm 22mm	—	—
JIS-B11	22mm 32mm	—	—
JIS-B10	32mm 45mm	—	—
JIS-B9	45mm 64mm	—	—
JIS-B8	64mm 91mm	—	—
JIS-B7	91mm 128mm	—	—
JIS-B6	128mm 182mm	—	JIS-B6
JIS-B5	182mm 257mm	JIS-B5	JIS-B5
JIS-B4	257mm 364mm	JIS-B4	JIS-B4
JIS-B3	364mm 515mm	—	—
JIS-B2	515mm 728mm	—	—
JIS-B1	728mm 1030mm	—	—
JIS-B0	1030mm 1456mm	—	—

Furthermore, I propose to add all sizes from two international standards, which are not covered by the interoperability argument (as of early 2020).

ISO 217 specifies two A-based series for raw, uncut, untrimmed sheets, adding an R (for primary range) and SR (supplementary range) prefix, respectively. PDF Reactor does support systematic keywords for all of them.
The actual standard seems to only require the recognition of (S)RA0, (S)RA1 and (S)RA2, but othe oversizes to the sizes of the ISO 216 A series are encountered in practice. I think it makes sense to support at least as many sizes as the following standard for drawing paper.

ISO 5457 specifies drawing paper sizes, where the trimmed sizes with a T suffix are identical to the respective A series sizes, whereas the sides of untrimmed U sizes are 3 to 4 centimeters larger. The standard also specifies a fixed area for the drawing space resulting from 20mm and 30mm page margins, but does not assign monikers.

Proposal	Size	PDF Reactor
SRA0	900mm 1280mm	SRA0
A0U	880mm 1230mm	—
RA0	860mm 1220mm	RA0
SRA1	640mm 900mm	SRA1
A1U	625mm 880mm	—
RA1	610mm 860mm	RA1
SRA2	450mm 900mm	SRA2
A2U	450mm 625mm	—
RA2	430mm 610mm	RA2
A3U	330mm 450mm	—
(SRA3)	320mm 450mm	SRA3
(RA3)	305mm 430mm	RA3
A4U	240mm 330mm	—
(SRA4)	225mm 320mm	SRA4
(RA4)	215mm 305mm	RA4
—	160mm 225mm	SRA5
—	152mm 215mm	RA5
—	112mm 160mm	SRA6
—	107mm 152mm	RA6
—	80mm 112mm	SRA7
—	76mm 107mm	RA7
—	56mm 80mm	SRA8
—	53mm 76mm	RA8

All American sizes, which have not already been specified in CSS, fail at least one of the three stated criteria, because their edges measure a simple number of half inches and are even often known only by those numbers (which are generally assumed to be exact).

The only popular metric sizes that are known by integer numbers are photographic prints (i.e. traditionally 9×13, 10×15, 13×18, 20×30), which, apparently, are rather approximate in fact, because they are really based on rounded inch-based specifications in ISO 1008 (see Wikipedia).

Start with the css-page size definition and compare its currently standardized keywords with the proposed ISO, JIS, and related paper-size tables in this issue. Done would require a resolved CSS Working Group decision on the scope and naming, followed by updating the relevant specification text; no source file or test entry point is identified here.