Your word proces­sor as­sumes that a word space marks a safe place to flow text onto a new line or page. A non­break­ing space is the same width as a word space, but it pre­vents the text from flow­ing to a new line or page. It’s like in­vis­i­ble glue be­tween the words on ei­ther side.

Put a non­break­ing space be­fore any nu­meric or al­pha­betic ref­er­ence to pre­vent awk­ward breaks. Re­call this ex­am­ple from para­graph and sec­tion marks:

In the top ex­am­ple, nor­mal word spaces come af­ter the § and ¶ sym­bols, and the nu­meric ref­er­ences in­cor­rectly ap­pear on the next line.

In the bot­tom ex­am­ple, non­break­ing spaces come af­ter the § and ¶ sym­bols. This time, the sym­bols and the nu­meric ref­er­ences stay together.

Use non­break­ing spaces af­ter other ref­er­ence marks (Ex. A, Fig. 23), be­tween the dots in Blue­book-com­pli­ant el­lipses, and af­ter copy­right sym­bols (see trade­mark and copy­right sym­bols).

In ci­ta­tions, use your judg­ment. In the ci­ta­tion Fed. R. Evid. 702, you can put a non­break­ing space be­fore the 702 so it won’t get sep­a­rated from Evid. But cer­tain ci­ta­tion for­mats, like the Cal­i­for­nia Style Man­ual, don’t use spaces in the ab­bre­vi­ated name of the source (116 Cal. App.4th 602). In those cases, the non­break­ing space can cause more prob­lems than it solves be­cause it cre­ates a large, un­break­able chunk of characters.