A quad, or quadrat, is a metal object, and there is no question of it being condensed, expanded, or altered in width.
The usage notes (and the ones under em space and en space) imply a second sense of quad “in electronic publishing.” But quads are not used in phototypesetting or digital publishing, and today's designers don't know what they are. Yes, the Unicode standard has named two characters after the em quad and en quad, but these are not used in publishing, and I doubt that their names are attested per CFI. Some publishing systems do have distinct quad left (align left) and quad right (align right) controls, named after the distinct verb sense, as in to quad out a line.
OED (draft 2009) puts the quad “[i]n letterpress printing,” and calls it “now chiefly hist.”
M–W: “a type-metal space that is one en or more in width”
Webster's Revised Unabridged: “A block of type metal...”
Monotype, Fonts.com Glossary, s.v. em space: “A space equal to the measure of the em at a given point size. In composition with metal type, it was created by the em quad, a block of type that was less than type high so that it would not print. . . . Em quad is a synonym”; s.v. quad “See em space, en space.
So, if the sense of electronic quads can be attested per CFI, then can we also find a reference supporting the encyclopedic discussion of the difference between quads and spaces? – at best this seems encyclopedic and non-defining, but the facts look arguable to me. If the sense can't be attested, then let's remove the usage notes about it. —MichaelZ. 2009-04-24 02:34 z
At least two Microsoft Press books include this sentence: "Fonts use a break character called a quad to separate words and justify text." Equinox◑ 18:53, 24 April 2009 (UTC)
And this has been copied to a few other websites. It seems to be related to the typographic quad, but I can't find another reference to this precise sense. A fuller quotation:
The blank character is the first character in the Windows character set. It has a hexadecimal value of 0x20 (decimal 32). . . . Fonts use a break character called a quad to separate words and justify text. Most fonts using the Windows character set specify that the blank character will serve as the break character.
0x20 is the regular space, corresponding to Unicode U+0020. So in this context (handling fonts at the program code level?), the regular space is usually the “quad.” Or maybe it's a mistake.
Also confirmed that the Unicode characters for em quad and em space are equivalent and identical:
U+2003 EM SPACE, also known as the “em quad,” is a space one em wide. . . . U+2001 EM QUAD was a mistaken duplicate encoding of the same thing and now has a singleton canonical decomposition to this character. (Gillam 2003, Unicode Demystified)
\quad is a command in TEX digital typesetting, representing “a quad space”, where \enspace, \quad, and \qquad (repr. en space, quad space, and two quad spaces) have identical properties, corresponding to letterpress quads, contrasting with the several smaller word spaces which expand in justification. “Note that \quad, \qquad, and \enspace have no stretch and shrink associated with them.” (Clark 1992, A plain TEX primer; see also the accompanying table) —MichaelZ. 2009-04-25 02:42 z
Striking: It's not clear to me what exactly you would like verified. You seem to be inferring a sense from the usage notes, and requesting that said inferred sense be verified? If so, feel free to convert the usage notes into an actual sense, and then RFV said sense. Otherwise, it's not clear to me what cites you're looking for, exactly. —RuakhTALK 19:25, 4 January 2010 (UTC)