Strange regular expression behavior in php

Question

Regular Expressions

php regex:
var_dump(preg_match("/^\d{0,10}$/","01234567")); => 1 (any number between zero and 10)
var_dump(preg_match("/^\d{,10}$/","01234567")); => 0 (any number between nothing and 10)

PHP doesn't understand incomplete quantifiers?

Answer 1

{,N} is not a valid quantifier in any language (unlike {N,})

Answer 2

php.net/manual/en/regexp.reference.repetition.php
An opening curly bracket that appears in a position where a quantifier is not allowed, or one that does not match the syntax of a quantifier, is taken as a literal character.
For example, {,6} is not a quantifier, but a literal string of four characters

Answer 3

{,n} is not a valid quantifier. {n,} and {n,m} can be used.

Answer 4

that is, if it is not valid, then it turns out to be useless ...