Access custom attribute for Web API parameter Help Documentation

I was trying to access the custom attribute from Library project for my WEB API Help Documentation for parameters additional Information.

For Example==> If that regular expression accepts only 7 digits, I need to show in the WEB APi parameter addition information like For Example("1234567") along with regular expression auto generated documentation.

How can I access property custom attribute from one library project to WEB APi help Documentation for parameters additional Information, Especially for regular expressions?