Given the string: `the_number_10_is_important`, I want to capture `_10_` and exclude `10`.

I essentially want to replace all underscores surrounding digits with brackets.

`_\d+_` selects `_10_` is my starting point. I'm trying to use [lookaround](https://www.regular-expressions.info/lookaround.html) or a non-capturing group eg. `_(?:\d+)_`