find a document bug for expr

[hanpingtian]

hi,

I think I have found a document bug for expr:
in the info page of "String expressions", it says "`expr' supports
pattern matching and other string operators.  These have *lower*
precedence than both the numeric and ...",.
But I think the string expressions have *higher* precedence than
numeric operator. For
example, this expression should return 17:

$ expr ' a16b' : ' a\(..\)b' + 1

And in "Numeric expressions" and "Relations for expr", there are the
same problems as this: they state the wrong precedence.