# How to use Discourse regexes with watched words?

**URL:** https://meta.discourse.org/t/how-to-use-discourse-regexes-with-watched-words/61522
**Category:** Support
**Created:** [24 באפריל,‏ 2017,‏ 9:25pm UTC](https://meta.discourse.org/t/how-to-use-discourse-regexes-with-watched-words/61522 "2017-04-24T21:25:19Z")
**Posts on this page:** 1
**Showing post:** 9

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### Author: ![justin](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/justin/32/157614_2.png) [@justin](https://meta.discourse.org/u/justin)
#### Post date: [29 במאי,‏ 2019,‏ 6:04pm UTC](https://meta.discourse.org/t/how-to-use-discourse-regexes-with-watched-words/61522/9 "2019-05-29T18:04:46Z")

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### Discourse Regexes (Watched Words)

> 📣 To use regular expressions (regex) in watched words you must first turn on the `watched words regular expressions` site setting.

Discourse by default matches all uppercase and lowercase forms of a word entered as a regular expression. That is,

> `thread`

This will match `thread`, `THREAD`, and `thReAd`.

> `(t|7)hr(3|e)(4|a)d`

This will match all of the cases above, plus `thr3ad`, `7hread`, and `thr34d`.

> `threads?\S+`

This will match `thread` and `threads` but not `threaded` or `threading`.

However, 🛑 there’s a glaring error in _ALL_ the above examples! The words `threadlike` and `unthreading` are matched (`un▪️▪️▪️▪️▪️ing`), even though they’re not referring to `thread`. How do we fix that?

We’d have to amend our regex to handle word boundaries.

> `\bthreads?\b`

This looks for boundaries around the word so that `unthreading` or `threadlike` aren’t caught by the filter, but `thread` and `threads` still are.

For handling Unicode characters

> `gr(ü|ue)(ß|ss)e`

This matches all commonly spelled forms of the word grüße — including `gruesse` and `GRÜSSE`

Say we want to block the word `Über`, but not `Übersicht`. Using word boundaries like `\b(ü|ue)ber\b` doesn’t work because some of the JavaScript regex word flags don’t handle Unicode characters.

Instead we have to make our own boundaries.

> `(?:^|\s)(ü|ue)ber\b`

This will now appropriately match `Über` and `ueber`, but not `Übersicht` or `uebersicht`.

### A final warning

Regex is extremely powerful and thus dangerous. An incorrectly written regex statement can cause issues for your users. Test your regex statements on non-production instances before going live.

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_[View the full topic](https://meta.discourse.org/t/how-to-use-discourse-regexes-with-watched-words/61522)._