Is your feature request related to a problem? Please describe.
There is an (now obsolete) addon that allows players to press TAB to auto-complete nicknames: Nick Completer

In the same way, it would be pretty awesome to be able to press the TAB key (inside Action Blocks, Variables boxes, ...) to see the spell name automatically completed. It would save a lot of time while typing spells in the macro.

Describe the solution you'd like
Auto-completion of spell names by pressing TAB key.

Additional context
Maybe you could use the code of the Nick Completer addon (link above) as an inspiration to create your own "Auto-Completion" feature?

Mock-up

The player types the first characters of the spell name ("Asp" for Aspect), then press the TAB key to make the rest of the spell name appear:

Not possible im afraid. There is very limited Predictive Text capability available.

TAB moves you to the next box.
It doesn't, here. I tested on the Configuration tab before submitting this suggestion.

I have just retried, pressing TAB still doesn't move to the next box. 🤔
Just in case, I have removed TAB from my key bindings (it was associated to Target Ennemy) and I've retried. Same, it doesn't move to next box.

But "TAB" was just a suggestion. Any key (of you choice) could have performed this auto-completion.

For reference:

I have found another project that features auto-completion: Slashhelp (Updated: 03/27/21)

I have found it thanks to this forum: https://www.wowinterface.com/forums/showthread.php?t=40555

Here is a video of it in action: https://www.screencast.com/t/gRczrQJo3