The TextAttributeSet attributes need some clarifications.

1. The attributes are defined in a stateful manner. For example,
   SWAPCOLORS_DEFAULT, SWAPCOLORS_OFF, SWAPCOLORS_ON are defined as
   values for SWAPCOLORS. This definition gives the idea of stateful
   information for specifying a swapcolors attribute between attributes
   runs. However, attributes are not handled in a stateful way.

2. SWAPCOLORS shouldn't require that both foreground and background be
   specified to be effective. It should simply swap foreground and
   background colors regardless of being explicitly specified or not.

3. The documentation should clarify mandatory attributes to be set to
   invoke each method.

4. The documentation should be improved to clarify keys and values.

5. FAMILY_ALL is not documented.