I could suggest :
--8<---------------cut here---------------start------------->8---
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -3013,7 +3013,7 @@ but before count is used up, nil is returned. */)
DEFUN ("backward-prefix-chars", Fbackward_prefix_chars,
Sbackward_prefix_chars,
0, 0, 0,
doc: /* Move point backward over any number of chars with prefix
syntax.
-This includes chars with "quote" or "prefix" syntax (' or p). */)
+This includes chars with "quote" syntax class (') or "prefix" syntax flag (p).
*/)
(void)
{
ptrdiff_t beg = BEGV;
--8<---------------cut here---------------end--------------->8---
Is it any better ?