Like everything else in
Mathematica the textual forms of expressions can themselves be represented as expressions. Textual forms that consist of one-dimensional sequences of characters can be represented directly as ordinary
Mathematica strings. Textual forms that involve subscripts, superscripts and other two-dimensional constructs, however, can be represented by nested collections of two-dimensional boxes.
If you use the notebook front end for
Mathematica, then you can see the expression that corresponds to the textual form of each cell by using the menu item.