Regex Explanation required

My Regex:

\d{0,2}\.?\d{0,3}r?em

string to match:

12123rem

Why is it matching 5 digits?

I want it to match the following pattern only:
12em or 12 rem or 12.345em or 12.345rem

up to 3 decimal places only.

>Solution :

Try this one:

^\d{0,2}(\.\d{1,3})?\s?r?em$

Here is a demo

• ^ – assures we are at the begining of the string
• ^\d{0,2} zero up to two decimals after begining of string
• (\.\d{1,3}) optional group of 1 up to 3 digits with . in front
• \s? optional whitespace character
• r? optional r character
• em mandatory em
• $ end of the string