Out of all the encoded fixed-width spaces, this is the one whose purpose completely eludes me.
The Unicode Standard defines it thus: “U+2008 punctuation space is a space defined to be the same width as a period.” [Version 8.0 p. 266]
I have seen Adobe
documentation about their Insert White Space > Punctuation Space (which does indeed insert the U+2008 codepoint) described as “Same width as an exclamation point, period, or colon in the typeface” — which is, of course, somewhat arbitrary, given that in any given font those three punctuation marks are not necessarily going to have the same advance width.
Does anyone know precisely why the Unicode Consortium chose to encode this space and what the proposed usage was that made this a convincing case for inclusion?
I have my own thoughts about what such a space could/should actually be useful for, practically speaking; but they don’t necessarily coincide with the minimal definition, and I have no reason to believe that others would expect it to be designed for such usage.
Comments
The Adobe description though is indeed wishy-washy.
Etymology
Used to give consistent presentation of quotation marks irrespective of comma or period placement.
Noun
punctuation space sg
But I can imagine the Unicode punctuation space being intended for use in traditions that feature some spaced punctuation marks, like with some French punctuation. However, I doubt that any French typographers view that codepoint in that way. I believe they tend to have their own conventions, using other fixed-width spaces, like the thin space.
If that was indeed the intention of the punctuation space, it would be nice to have it confirmed in some Unicode documentation. And have French experts confirm that the width of a period is indeed the proper reference (which I kinda doubt, but who am I to say).
To expand upon this a little: to be really practical for tabular use, in my opinion, such a space would be fixed across styles (RIBBI at least), which is what I personally advocate for tabular figures. At which point, if it is going to align with default period and comma, that means those punctuation would also have to be duplexed across RIBBI styles, which begins to place an unnatural constraint on them for regular, non-tabular purposes.
It is not uncommon for fonts to feature separate tabular punctuation for such purposes, often on half-tabular width. In which case, such a half-tabular space could be encoded as the U+2008, I suppose. But I’m not sure the value of having that encoded, given that the tabular punctuation are not separately encoded. Usually these are just deployed with an OTL feature.
Which brings me back to my question: What is the real purpose for which Unicode enshrined such a space?
It costs nothing to include all available Unicode spaces from em-space to zero-width space in one's fonts, so I usually do. It's a simple cut and paste operation, with some minor adjustments needed for figure space and punctuation space.
In practice, in my publications I sometimes use the zero-width space or the hair space, but have not used the punctuation space much, if at all.
Looking at my fonts, I probably don't always remember to adjust for the font. Garava is my base font, which I use for testing FontCreator, and learning how to design OpenType features etc. For that, the spaces are all what they should be:
" Indeed. These fixed-width and other special spaces all date to Unicode 1.0, and their proximate source was the Xerox Character Code Standard. (XCCS 1980)
The punctuation space can be traced to:
XCCS 0xEE 0x24 "Punctuation space (fixed, device dependent, and normally nonprinting)"
The "normally nonprinting" note that is associated with this character (and several others of these fixed-width spaces) may have something to do with the Xerox Star implementation -- not sure. You'd have to check with Joe Becker to see if he recalls how the Xerox systems implemented these spaces.
--Ken"
Interesting that the XCCS definition provides no particular reference for the fixed width itself (not referencing a period or comma or anything).
I read “nonprinting” as meaning that there is no printing portion of this character — i.e., it is an encoded white space.
Not sure what to make of “device dependent.” Presumably the fixed-width spaces that are defined as rational increments of the em — e.g., en space, four-to-em space, et al. — are device independent. So, what’s so device-dependent about a punctuation space and who used it for what?
Curiouser and curiouser.