Regular Expression for Census Tracts - regex

Question

I am working on making sure a form input is parsed correctly through google forms and I was trying to use my limited regex knowledge to make sure that people do not input tracts incorrectly.
usually a tract is given in an example such as 5129.01
All tracts in the county start with 5, have a second character that is either a 0 or a 1,and if it is a 1, the third character is either [0 - 3] else its [0-9].
I have a working expression but I would like to ensure that if the second character is a 1 the user wouldn't be able to enter a tract like 5150.01
This is what I have:
^5[0-1]([0-9]{2})(\.([0-9]{2}))?$
and this is what is not working:
^5[0-1](?(?<=1)\d|[0-3])(\.([0-9]{2}))?$
Any help would be appreciated thanks

Answer 1

I hope this answers your question, please comment and I can edit accordingly.
The pattern:
^(?:51[0-3]|50[0-9])[0-9](?:\.[0-9]{1,2})?$
A visual representation:
HTML implementation:
<input name="example" pattern="^(?:51[0-3]|50[0-9])[0-9](?:\.[0-9]{1,2})?$">
Value validation examples:
+----------+--------+
| Value | Status |
+----------+--------+
| 51 | fail |
| 510 | fail |
| 5101 | pass |
| 5111 | pass |
| 5121 | pass |
| 5131 | pass |
| 5141 | fail |
| 5102. | fail |
| 5102.1 | pass |
| 5102.12 | pass |
| 5102.123 | fail |
| 50 | fail |
| 500 | fail |
| 5001 | pass |
| 5011 | pass |
| 5021 | pass |
| 5031 | pass |
| 5041 | pass |
| 5051 | pass |
| 5061 | pass |
| 5071 | pass |
| 5081 | pass |
| 5091 | pass |
| 50911 | fail |
| 5092. | fail |
| 5092.1 | pass |
| 5092.12 | pass |
| 5092.123 | fail |
+----------+--------+