This mixin implements the basic functionality needed for text% objects in the framework.
The class that this mixin produces uses the same initialization arguments as it's input.
The linespacing argument sets the additional amount of space (in DC units) inserted between each line in the editor when the editor is displayed.
See set-tabs for information about tabstops.
A new keymap% object is created for the new editor. See also get-keymap and set-keymap.
A new style-list object is created for the new editor. See also get-style-list and set-style-list.