A Selector which describes an area of interest in another thing using start and end values, interpreted as positions in a character stream.

Position 0 is the position preceding the first character, position 1 is the position after the first character but before the second, and so on. “Character” here means “Unicode scalar value”, regardless of underlying encoding. This selector selects on a plaintext character stream; markup must be ignored when selecting. In X·M·L and H·T·M·L, that means it selects only on the sequence of text nodes in the document, in document order, after all entities have been expanded.