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[...] TextMate seems to show tabs and line endings but not any more of the non-printing characters that BBEdit shows

It does show unprintable characters, but not spaces.

It's good to know I wasn't doing something wrong. However, if the functionality exists [and has already been written/tested] why keep it out of a release?

Trust me, I want to fall in love with TextMate, but there's some things that can't yet be done in TextMate -- I find myself jumping back to BBEdit in order to accomplish these tasks.

I found that to look too busy and the spaces should be indicated by where there are no other ,,invisibles% shown

I respect the consideration to keep the application lean and fast, but when should a developer's personal preference get in the way of what his/her end user's want out of a product?

(I know there are requests for configuration here).

A simple option or preference would be a welcome addition and wouldn't require people to use it. BBEdit conditionally allows one to show invisibles and then selectively choose whether or not spaces are shown.

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I was able to find the ShowInvisibles Bundle for TextMate that aims to highlight tabs and spaces in different colors but it doesn't appear to work with my setup and/or preferences.

It was created prior to the theme system. What it does is give a certain scope to spaces (and other characters), but for that to show, you would need to add a theme rule for it.

This information is encouraging, but the bundle doesn't come with any documentation or configuration instructions, only to edit the Invisibles.plist to suit ones' needs.

Could you put together an example of a theme rule that would highlight the spaces in a document using this bundle?