Regular Expressions 101

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"
^[0-9]{10,13}$
"
mg
^ asserts position at start of a line
Match a single character present in the list below
[0-9]
{10,13} matches the previous token between 10 and 13 times, as many times as possible, giving back as needed (greedy)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
$ asserts position at the end of a line
Global pattern flags
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
mg

Test String