Intersection, Union, and Difference

Constraints that must be simultaneously true of a region are expressed by separating the constraint expressions with commas. The region set matched by S₁, S₂, ..., S_n is the intersection of the region sets matched by each S_i. For example just after "From:", just before "\n" describes all regions that start immediately after a ``From:'' caption and end at a newline.

Alternative constraints are specified by separating the constraint expressions with ``|''. The region set matched by S₁ | S₂ | ... | S_n is the union of the region sets matched by each S_i. Set difference is indicated by but not. The region set matched by S₁ but not S₂ is the set that matches S₁ after removing all regions that match S₂.