A nonbreaking space is a special character that’s the same width of a normal space, but the word processor won’t put a line break or page break where the nonbreaking space is. It’s like invisible glue between the two words before and after.
That way, you can avoid references that look like Bus. & Prof. Code §
17200. With a nonbreaking space, the 17200 is guaranteed to appear on the same line as the section mark, like this: Bus. & Prof. Code
§ 17200.
Windows Word: CTRL + SHIFT + [space]
Windows WP: CTRL + [space]
HTML:
A nonbreaking space should usually be used in front of any numerical or alphabetic reference. It should definitely appear after paragraph marks and section marks. It should also appear after other abbreviated reference marks that might appear in your document, such as Ex. A or Fig. 23, or citations like Fed. R. Evid. 702.
(Be warned that certain citation formats, for instance the California Style Manual, don’t use spaces in the abbreviated name of the source, e.g. 116 Cal.App.4th 602. In those cases, the nonbreaking space can cause more problems than it solves. Use your discretion.)
I make heavy use of non-breaking spaces, but unfortunately they don’t really play nicely with justified text (at least in Word). When the justification forces Word to expand the width of the spaces between words, it only expands the normal spaces, not the non-breaking spaces. As a result, you sometimes get odd-looking lines that wind up something like this:
This…is…a…sentence…where…Bus…&…Prof…Code…§.17200…is…cited.
Of course, there are also folks who use that glitch as a feature — they want to put extra space at the start of a line, but don’t want to use the full tab space (at least with default tab spacing), and regular spaces might expand due to justification, so they use non-breaking spaces instead. Incidentally, it might be useful if you added an entry on setting and using tab stops to align things – and perhaps Word’s “first-line indent” and “hanging” settings in the paragraph dialog – rather than just default tab stops and spaces (which is what I commonly see).