From: Christoph Päper via GitHub <sysbot+gh@w3.org>

Date: Wed, 03 Aug 2016 21:02:04 +0000

To: public-css-archive@w3.org

Message-ID: <issues.opened-169233140-1470258122-sysbot+gh@w3.org>

Date: Wed, 03 Aug 2016 21:02:04 +0000

To: public-css-archive@w3.org

Message-ID: <issues.opened-169233140-1470258122-sysbot+gh@w3.org>

Crissov has just created a new issue for https://github.com/w3c/csswg-drafts: == [css-syntax][css-values] Awkward Decimal Fractions and Non-Finite Values == As noted in #315 by @dauwhe and @plinss and in #309 by me, some existing CSS units do not play well with decimal floating point numbers. These are **vulgar fractions** on the one hand, which can become rather **long but terminating**, like 1/16 = 0.0625, or **repeating**, like 1/12 = 0.08_3, and **irrational constants** on the other hand, e.g. π = 2·τ = 3.1415…, √2 = 1.4142… or φ = ½+√1¼ = 1.6180… The English typogaphical units (inch, pica and point) in particular are traditionally used either with vulgar fractions and a single unit (`in`) or with integer amounts of a mix of units (`pc` and `pt`, e.g. “1p2” for `14pt`). Both can be achieved by using `calc()`: padding: calc(1in / 16); font-size: calc(1pc + 2pt); Unless we add keywords for some common (quasi) constants to be used within `calc()`, the same approach doesn’t work for irrational numbers: color: hsl(calc(2 / 3 * pi), 50%, 100%); size: 8.5in calc(8.5in * sqrttwo); aspect-ratio: calc(phi); /* or 'golden' */ This is obviously not quite as convenient as handwritten or typeset values, which would look a bit like this if approximated with CSS syntax: padding: 1/16in; font-size: 1pc2; I tried to show some possible solutions in #315 which I’ll repeat here for convenience and annotation. The example value was “3p4½” or “9/16 inch” in classic notation. This can be expressed with `calc()` in several ways: calc(3pc + 4.5pt) calc(3pc + 9pt / 2) calc(3pc + 3pc / 8) calc(9in / 16) A natural adoption of the “p notation” would be function syntax: p(3, 4.5) p(3 4.5) p(3 p 4.5) p(3pc 4.5pt) p(40.5) Parentheses or brackets might provide a way to escape restrictions by the core grammar: (3 p 4.5) [3p4.5] If the core grammar needed to be changed, there would be several ways it could be done that still mimic the traditional notation. The value for the secondary unit could be added either between the primary value and unit or after them, in both cases with a punctuation character used as separator. The third option would be similar to exponent `e` syntax with `p` and would be specific to the pica-point case. 3-4.5pc 3+4.5pc 3:4.5pc 3,4.5pc 3/4.5pc 3&4.5pc 3..4.5pc 3pc-4.5 3pc+4.5 3pc:4.5 3pc,4.5 3pc/4.5 3pc&4.5 3pc..4.5 3p4.5pc 3p4.5pt If it was possible to put two values around a base unit symbol like `pc` to specify the fractional value in the “sub-unit”, this would apply to other units as well and there needed to be agreement which units combine (e.g. `mm` and `q`): 3pc4.5 40pt10 0in3.375 14mm1.15 57q37.5 3cc2.1 Conversion to different units may bring nicer values, but does not fit the work flow. In some cases, integer values or nice fractions could be achieved only with additional units 3.375pc 40.5pt 0.5625in 14.2875mm 57.15q 810twip 38.1dd 14287.5um Unicode characters beyond Basic Latin would cover several use cases (including constants), but probably not all of them. (Note the fraction slash U+2044.) 3⅜pc 40½pt 9⅟16in 9⁄16in 9÷16in It would be *nice to have* a common solution to these related problems. I’m in no way claiming that I’ve already found it. I’m also not preferring one particular option out of the presented ones. Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/378 using your GitHub accountReceived on Wednesday, 3 August 2016 21:02:25 UTC

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