//gsub(/\<b*/,"") on "abc" will reach this point, advance to "bc"
//... and will erroneously match "b" even though it is NOT at the word start.
//we need REG_NOTBOW but it does not exist...
+//TODO: if EXTRA_COMPAT=y, use GNU matching and re_search,
+//it should be able to do it correctly.
/* Subtle: this is safe only because
* qrealloc allocated at least one extra byte */
resbuf[residx] = *sp;