Tektronix graphics support

[rbanffy]

Is your feature request related to a problem? Please describe.
This is not related to any problem I've found, but from a completeness point of view, it'd be useful to describe graphical instructions for supporting terminals such as xterm or the Digital VT-x3x or x4x series.

Describe the solution you'd like
Capture the mode change command (to enter and leave Tektronix mode) and switch to displaying descriptions for the Tek 401x protocol.

Describe alternatives you've considered
None, since this would be an extension of the functionality.

Additional context
There is at least one other graphics description language that might be worth looking into - ReGIS. Any support for multi-mode protocols would be wise to include space for expansion.

[meowgorithm]

Tektronix and ReGIS support would be awesome. This is likely not something we'd be able to implement in the short term, but if you're interested in contributing the feature you are more than welcome to go for it!

[rbanffy]

I must confess this was done in an "enlightened self-interest" state of mind (I promised to contribute Tek support to VTE). I have less time to contribute than ideal, but it'll be a pleasure to do my best to help.

[meowgorithm]

That warms my heart. Let us know know if you need any pointers!