Navigation by Up/Down arrows

[FoggyFinder]

Describe the solution you'd like
Navigation in arrow direction like it is in MathQuill. For example, when pointer in the last atom of an exponent then down arrow moves pointer on one level down.

Difficulty: How difficult would it be? (Trivial, Very Easy, Easy, Moderate, Hard, Very Hard, Tedious, Backbreaking)
Easy.

Additional context

[Happypig375]

This is covered by Left/Right arrows.

[charlesroddie]

This is covered by Left/Right arrows.

Left/right is enough to enter formulas but for superscripts/subscripts/fractions it would be preferable & normal to use up/down.