I would expect that Beyond Compare would ignore differences based on tabs vs spaces if in the Session Settings/Importance Tab, I check the boxes labeled Leading Whitespace and Embedded Whitespace while comparing text files using the default format. Neither checked nor unchecked causes those differences to be ignored.
What am I missing?
The checkboxes there are controlling what's important to the comparison. Whitespace will be important if they're checked and unimportant if they're unchecked. They do only affect text that doesn't match something else in the grammar though. If you're comparing C++ code, for example, and the whitespace occurs at the end of a comment line it will be classified as a comment instead.
Assuming it's classified as "unimportant" correctly, BC will still show it as a difference, but will show it in blue rather than red. You can hide unimportant differences using the View->Ignore Unimportant Differences menu item, which will make them appear using the matching coloring and filter as such.
If you're still having trouble you'll have better luck getting support if you email support@scootersoftware.com or post in our support forums at http://www.scootersoftware.com/vbulletin/ with a bit more information.
Go to: Tools -> File formats -> Grammar. Add a grammar item (the +) and then mark the Regular expression check box.
There you can add a regex matching the items you want and define the severity of them.
In general, this is very useful when you have some differences that are not important to you.
