Command/function names you want (not necessarily adopted as a command/function name):

• \overrightarrow{ math } (already implemented)
• \overleftarrow{ math }
• \overleftrightarrow{ math }
• \underrightarrow{ math }
• \underleftarrow{ math }
• \underleftrightarrow{ math }

Describe how you want the command/function to work.
Tensors are sometimes written in \overleftrightarrow.

Can other typesetting system (e.g. LaTeX) do the same thing? If so, provide a method to realize it.
Exactly the same as LaTeX.