Regular Expressions 101

Explanation

Pro

^start of line

Positive Lookahead(?=(?:\d\.?){0,16}$)

Non-Capturing Group(?:\d\.?){0,16}

{0,16}repeats the group contents below between 0 and 16 times:

\da Unicode decimal digit

\.?optionally matches the literal . (46₁₀ / 56₈ / 2E₁₆)

$end of line

\d+a Unicode decimal digit, repeated at least once

Non-Capturing Group(?:\.\d{1,3})?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d{1,3}a Unicode decimal digit, repeated between 1 and 3 times

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

^(?=(?:\d\.?){0,16}$)\d+(?:\.\d{1,3})?$

New

123
123.3
123.45
123.456
1111111111111.345
11111111111111.45

123.1234
11111111111111111
1111111111111111.
111111111111111.56