Regular Expressions 101

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/
(^[0-9]{1,11}$)|(^[0-9]{1,11}[\\.]{1}[0-9]{1,2}$)
/
gm
1st Alternative
(^[0-9]{1,11}$)
1st Capturing Group
(^[0-9]{1,11}$)
^ asserts position at start of a line
Match a single character present in the list below
[0-9]
{1,11} matches the previous token between 1 and 11 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
2nd Alternative
(^[0-9]{1,11}[\\.]{1}[0-9]{1,2}$)
2nd Capturing Group
(^[0-9]{1,11}[\\.]{1}[0-9]{1,2}$)
^ asserts position at start of a line
Match a single character present in the list below
[0-9]
{1,11} matches the previous token between 1 and 11 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)
Match a single character present in the list below
[\\.]
{1} matches the previous token exactly one time (meaningless quantifier)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[0-9]
{1,2} matches the previous token between 1 and 2 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
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
gm

Test String