Character design standards - Space characters for Latin 1
In traditional typesetting there were several characters used for word spacing. In digital font files the word space is a specific width character used for word spacing. Applications are responsible for adjusting the word spacing and character spacing to suit the current page layout. Many page layout applications allow for custom control of the word spacing through application specific functions. Unicode and OpenType fonts can provide similar custom word space glyphs or other glyph substitutions that will be portable to other applications.
In digital fonts there are only two kinds of space characters supported by most computers, the space and the no-break space.
Standard space characters
Advance width rule : The space's advance width is set by visually selecting a value that is appropriate for the current font. The general guidelines for the advance widths are:
The minimum value should be no less than 1/5 the em, which is equivalent to the value of a thin space in traditional typesetting.
For an average width font a good value is ~1/4 the em.
Example: In Monotype's font Times New Roman-regular the space is 512 units, the em is 2048.
For a wide width font a good value is ~1/3 the em.
Example: in Microsoft's Verdana the space is 720 units, Tahoma is 640 units. In Stephenson Blake's Wide Latin the space is 612 units. In all fonts the em is 2048 units.
The maximum width should be no greater than 1/2 the em, which is equivalent to the en space of a typeface.
The no-break space is the same as the word space character with the added functionality of providing a way to prevent two words from being separated by a line break.
Example: If the words 'Monotype's Arial' were at the end of a sentence and the author wishes for them to remain as a pair, a no-break space character could be used to keep the two words together.
Advance width rule : The advance width of the no-break space should be equal to the width of the space.
The no-break space is not the same character as the figure space. The figure space is not a character defined in most computer system's current code pages. In some fonts this character's width has been defined as equal to the figure width. This is an incorrect usage of the character no-break space.
Other space characters
The following characters are word space characters defined in Unicode. The majority of these characters are traditional typographic space values or characters that are related to other character's width criteria. Typographers used these characters to manually set type. Today computer applications and page layout systems alter space and set text. These page layout systems make use of only the space and no-break space. A typographer could use any of these characters to manually set text (when text is left or right justified) by substituting the word space U+0020 with one of these specific space characters.
Word space characters are also language and script dependent.
En quad U+2000 - equal to the en space and one half the em. In a noisy printing shop the en quad was called a 'nut' so it would not be confuse with the em quad.
Em quad U+2001 - equal to the em space.
En space U+2002 - 1/2 of the em space. 1024 units in a 2048 unit per em font.
Em space U+2003 - Traditionally defined as a space character with an advance width value equal to the current point size. In a 12 point font the em is equal to 12 point. In PostScript and TrueType fonts there are 72.0 points to the inch. This is not necessarily equivalent to the advance width of the uppercase M. In digital fonts font units are used to calculate point size. There are 2048 units in the em of a Latin 1 TrueType font.
Three per em space U+2004 - equal to 1/3 of the em space. 683 units in a 2048 unit per em font.
Four per em space U+2005 - equal to 1/4 of the em space. 512 units in a 2048 unit per em font.
Six per em space U+2006 - equal to 1/6 of the em space. 341 units in a 2048 unit per em font.
Figure space U+2007 - Standard setting is equal to the advance width of the figures, or figure zero.
Punctuation space U+2008 - Standard setting is equal to the advance width of the period U+002e and comma U+002c.
Thin space U+2009 - Standard setting is 1/5 of the em space. 410 units in a 2048 unit per em font. This should be language dependent. The standard language dependent setting for French is 1/8 of the em space. 256 units in a 2048 unit per em font.
Note : When traditionally typesetting the French language a word space is inserted before or after several punctuation characters. These characters are colon, semi colon, question, exclamation, right guillemets, and left guillemets. Commonly the preferred word space used is a thin space of 1/8 the em. Some French typographers prefer to use a larger space character of 1/4 the em with the colon and some other punctuation characters. OpenType supports character substitution and language dependant variants.
- Hair space U+200A - The thinnest space in a typeface. Recommended standard setting is 1/10..1/16 of the em.