How to typeset a “small” non-breaking space

Question

I can use ~ to produce a non-breaking space. But it is too large for me, and I would like a non-breaking space of the size of \, for example. Is it possible ?

Answer 1

There are two kinds of spacing that TeX can use: skips and kerns. The first sort of space can be flexible (the interword space is a skip, for instance), while the second one is rigid.

Both disappear at line breaks, but TeX will never break a line at a kern (unless it's followed by a skip), while it's willing to do it at skips. Therefore

word\,word

would never be broken across lines.

The command \, inserts a kern, precisely it's defined (in text mode) as

\kern 0.16667em

(where 1em is approximately the width of an uppercase "M", whence the name, or near the font size in points); so the space inserted by \, is 1/6 of an em.

Conversely, ~ is defined as a skip: its definition is \nobreakspace, which translates into

\leavevmode\nobreak\ 

(the last is "backslash+space"). There will be no line break at it, because the skip inserted by \<space> is preceded by so high a penalty that breaks are impossible (\nobreak translates into \penalty 10000).

You can space by inserting \kern yourself, but using a macro is preferable. If you need that the space is non breakable and flexible, use the same trick as ~:

\nobreak\hspace{.16667em plus .08333em}

would insert a space normally equal to 1/6 of an em, but stretchable to 1/4 of an em.

I left out the \leavevmode because such spaces should always be inserted between words. LaTeX takes that precaution, because users might use ~ in order to indent lines (which is not the best thing to do, though).