So the set of all tokens in a text is a subset of the set of all possible segments in that text. It is necessary to represent a text in such a way that both individual tokens and individual types can be identified. Segments and points form a basis for tokenisation. A critical point in a text is that which delimits two adjacent segments. Conversely a critical segment is that which is delimited by two points in the text.
Segments are, thus, located in time and space.
Segments can be observed, pointed to and given unique names. Segments and strings are not the same. Segments are instances of strings. Two segments may be instances of the same string. Segments may, thus, correspond to tokens, whereas strings correspond to types.