Do not use as a verb. As a noun, use only to refer to tabs on a ribbon, a webpage, in a dialog box, and so on.
For other uses, clarify the meaning with a descriptor. For example, say “the Tab key,” “a tab stop,” or “a tab mark on the ruler.” See also Webpage controls, dialog boxes, and property sheets (Chapter 5).
Use the Tab key to move through a dialog box.
Set a tab stop on the ruler.
Click the View tab.
Not Microsoft style
You can tab through a dialog box.
Set a tab on the ruler.
Do not use Table of Contents as the heading for the list of contents at the beginning of a document or file. Use just Contents instead. However, it is correct to refer generically to the table of contents.
Lowercase. In ...