{% include components/reference-button.html href="/segment-app/iam/roles/#pii-access" icon="media/academy.svg" title="PII Access" description="Use Access Roles to control who has access to the PII identified by your matchers." variant="related" %}

The matchers scan data coming from your Sources for PII based on both

exact-matching (and fuzzy-matching if you select 'Similar to' option).

As an example, if you have a custom matcher for detecting "credit card

number", it will also detect variations like "credit-card number", or

typos such as "creditt card number".

Our fuzzy matching uses[this public GitHub repository](https://github.com/imjasonmiller/godice)

to determine if it is a match. However, it will not detect all variations

and for those scenarios, you can use synonyms. You can add "credit card no",

"debit card number", or similar variations in the synonyms section.


Custom Matchers use[regular expressions](https://en.wikipedia.org/wiki/Regular_expression) (using the[Golang Regex Package](https://golang.org/pkg/regexp/)) to provide you great flexibility for your matching patterns.

-[RegExr](https://regexr.com/) - an online tool to experiment with regular expressions and test them

-[RegexOne](https://regexone.com/) - a tutorial which takes you from regular expression basics to advanced topics

-[Regexp Cheatsheet](https://devhints.io/regexp) - a handy cheatsheet to have nearby when you're writing regular expressions

Segment's exact matching and fuzzy matching do not detect all variations in the received keys

and for those scenarios, you can use synonyms. For example, for the value`credit card number`, you can add`credit card no`,

`debit card number`,`debit card no`, or similar variations in the synonyms section to classify those fields.