Mark. Mark is a special selection mode. It gives you the ability to select text multiply. To mark some text, select the text normally and apply Mark. To "deselect" the marked text, point to it with the cursor and use Mark again. The another way to disable marked selection is the Unmark all menu item. You can copy all marked text using Copy marked function.
Mark each n-th line - use this function to mark each n-th line. Type the number into the Famous text entry first.
Mark lines those contains a string - marks all lines those contains a string from the Famous text entry.