These commands are displayed only if a text layer is present.
In the Text to Selection drop-down list, the commands are identical to those of the Transparency sub-menu (in fact, the text is formed of areas of different transparency):
Text to Selection: Section 7.37, « Alpha to Selection »
Add to Selection: Section 7.38, « Add Alpha channel to Selection »
Subtract from Selection: Section 7.39, « Subtract from Selection »
Intersect with Selection: Section 7.40, « Intersect Alpha channel with Selection »