limit the string to. The result will be a unibyte string that is
shorter than LENGTH, but will not contain \"partial\"
characters (or glyphs), even if CODING-SYSTEM encodes characters
-with several bytes per character.
+with several bytes per character. If the coding system specifies
+things like byte order marks (aka \"BOM\") or language tags, they
+will normally be part of the calculation. This is the case, for
+instance, with `utf-16'. If this isn't desired, use a coding
+system that doesn't specify a BOM, like `utf-16le' or
+`utf-16be'.
When shortening strings for display purposes,
`truncate-string-to-width' is almost always a better alternative