That's often configurable. For example, in xterm: > -cc characterclassrange:value[,...] > This sets classes indicated by the given ranges for using in select

That's often configurable. For example, in xterm: > -cc characterclassrange:value[,...] > This sets classes indicated by the given ranges for using in selecting by words. See the section specifying character classes. and discussion of the charClass resource. (I haven't tried using this myself.)