Regular Expressions 101

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/
^(?!\.$)\d{0,10}(?:\.(?:\d\d?)?)?$
/
gm
^ asserts position at start of a line
Negative Lookahead
(?!\.$)
Assert that the Regex below does not match
\. matches the character . literally (case sensitive)
$ asserts position at the end of a line
\d{0,10}
matches a digit (equal to [0-9])
{0,10} Quantifier — Matches between 0 and 10 times, as many times as possible, giving back as needed (greedy)
Non-capturing group
(?:\.(?:\d\d?)?)?
? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
\. matches the character . literally (case sensitive)
Non-capturing group
(?:\d\d?)?
? Quantifier — Matches between zero and one times, as many times as possible, giving back as needed (greedy)
\d matches a digit (equal to [0-9])
\d?
matches a digit (equal to [0-9])
$ 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.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String