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The first one allows to build completers for commands consisting of several words e.g.  "BEGIN STATEMENT SET;" and the second one allows to unite them all together.

Cross dialect

Since there are at least 2 dialects in Flink (HIVE and DEFAULT). There could be a builtin dialect enum containing required info.
Taking current dialect it's possible to retrieve required info from that enum about quotes, comments and etc for parsing, highlighting and completion.

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So that means that adding a new dialect should be relatively simple.

Widgets

Jline allows to define widgets and bind them to key strokes.

Within a widget it is possible to define an action e.g. changing a property and invoke redisplay - this is how toggle of line numbers or switching highlight schema could be done

Summary

After this FLIP finishes, the sql client will have the options.

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