^{Mark menu}

Marks are used to allow particular files to be included or excluded from the comparison

Mark file marks the selected file

Mark pattern… leads to a dialog which allows you to specify a substring or a regular expression and have all the files that match this pattern marked.

"$" means "end of string"

"\\" means "\"

"\." means "."

Thus to mark all files with extension "obj" the expression should be "\.obj$".

Hide marked files removes from the displayed list all the marked files (and any future file as it becomes marked)

Toggle mark state marks all unmarked files and unmarks all marked files. If you want to select the files that you wish to see, mark them, hide marked files (they will disappear) and toggle the mark state (they will reappear and the rest will disappear).