Bear in mind, though, that alternate preferences and variations are not uncommon. Also, the capacity to apply some of these guides may only be possible when using professional page layout programs such as InDesign and QuarkXPress.
EN Dash – ALT (OPTION Mac), HYPHEN Key
Traditionally, this was a dash with a length 1/2 the point size, of the font in use. For 12 pt. type, the EN dash would be 6 points long. Now, the length is variable depending upon the style of a particular font.
The EN dash is used to replace the word “to” in expression of a range. For example:
New York – Chicago – L.A. or 1939 – 1944.
EM Dash — ALT, OPTION (Mac), SHIFT, + Key
This dash is used to show a grammatical pause, which is longer than a comma, but shorter than a period. The use of a space before and after is preferable as in: “Wait — I hear something!”. Many specialists advocate no space at all as in: “Wait—I hear something!”. The Em dash was traditionally twice as long as the EN; however, not all modern typeface styles conform.
A hyphen has only two uses. One is in hyphenated words. Also, hyphens occur as a word break at the end of a line of type. Watch for “ladders,” a line of 3 or more hyphens, in the margin. Always correct this distracting effect.
Never use two spaces after a period. Also if copy contains a lot of abbreviations and has a “peppered” look, it is acceptable to eliminate the period, except for sentence breaks. Also, when setting times, use lowercase abbreviations, without periods (e.g. 12:45 pm).
Ellipses . . .
This punctuation is used to represent an interruption of thought or speech. The dots require space, in between, which is achieved by tracking and not by insertion of a space. It a space is used a line break could occur in the middle of the ellipses.
Commas, Apostrophes and Hash Marks
It is difficult to illustrate this on a web page as commas and apostrophe’s usually appear as hash marks on the screen. Apostrophes and Commas are usually angled or curved characters, styled appropriately for a particular font. They ought to be used for quotations and contractions. Software programs have an enabling preference called “Smart Quotes,” which automatically applies the correct mark.
Hash marks, “, are used to indicate feet and inches (2′ 6”), or sometimes degrees (as in a 90′ angle).
Punctuation marks in large headings need to be reduced in size and kerned closer to the type, because, when type faces are enlarged the punctuation is over-emphasized. Punctuation may often be eliminated, in headings, and be replaced by line spacing (i.e. leading)
Fractions should not be set using standard number characters. They should be set using fraction characters from an alternative font or manufactured using superscript and subscript.
Spell numbers which begin sentences.
Never set paragraph indents using the default tab setting. Indents should be one EM ore more. An EM space is the same as the point size of the font in use (e.g. given 8 point Helvetica, a 2 EM indent would be 16 points). Also regarding indents, many typesetters prefer not to indent the first line of text after a heading or subheading.
The intent of this and the two above referenced articles has been to spotlight the importance of typography and reveal some of its intricacies. This discussion, is by no means complete, nor would all of the suggested guides, though technically and professionally accurate, be accepted by all authorities. Finally, remember that consistency and readability remain the most important considerations in typography.