A non-breaking space is a separating character intended to keep adjacent text together during ordinary line breaking. The common Unicode character is U+00A0 NO-BREAK SPACE. It has line-break class GL; the surrounding rules determine which boundaries are prohibited.[ref]
Unicode Line Breaking Algorithm by the Unicode Consortium. §5.1, GL class; rules LB12 and LB12a
For an example,
25\u00a0µm is a visible spelling of an escape notation for a number, U+00A0, and a micrometre symbol. The actual text 25 µm keeps the number and unit together at that separator. Ordinary 25 µm instead uses U+0020 SPACE and can provide a wrap opportunity there. Neither choice fixes the physical width of the gap in every computer font.The rule is local. In the sequence
A\u0020\u00a0B, a break after the ordinary space can still be allowed, leaving the non-breaking space on the following line. Thus inserting U+00A0 does not make an entire text paragraph unbreakable.[ref]Unicode Line Breaking Algorithm by the Unicode Consortium. GL description: SPACE before NO-BREAK SPACE; LB12a exception
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