\spacefactor: Extra space after punctuation ¶Synopsis (but rarely used this way; see subsections):
\spacefactor=integer
Influence LaTeX’s stretching and shrinking of interword glue. With
rare exceptions, only American English documents need this feature,
and in those few cases where the defaults need to be overridden, the
\@ command usually suffices.
If the xspace package is being used, that changes all the rules
and what is described here does not necessarily apply (see xspace package).