Rik Kabel via ntg-context schrieb am 15.11.2021 um 19:06:

So, some follow-up questions:

1. What do you mean by "only one setup" in the description of directsetup and fastsetup? I have examples of using two different directsetup in one after key, so it does not seem to mean that.

With \directsetup, \fastsetup and \setup (I'm correcting Hans here) you can pass only the name of a single setups-environment as argument, e.g.

\directsetup{my_fancy_setup}

while \setups allows you to pass a list of names, e.g.

\setups[custom_setup_a,custom_setup_b,...]

2. What is meant by saying that directsetup supports gridsnapping? Do you mean that fastsetup does not? (If that is the case, should a module writer not use fastsetup because it might be used in a document that requires a grid?)

The \startsetups environment has a optional argument which accepts (at the moment) the "grid" keyword to set values which are only used when grid snapping (\setuplayout[grid=yes]) is enabled, e.g.

\startsetups [grid] [my_fancy_setup]
    % settings which are used when grid mode is enabled
\stopsetups

\startsetups [my_fancy_setup]
    % settings which are used when grid mode is disabled
    % or when no grid related setups with the same name exist
\stopsetups

When you now use \directsetup{my_fancy_setup} (or \setup[...]) ConTeXt checks if grid mode is enabled and selects the right settings but \fastsetup never performs this check and always uses the non grid settings. The \fastsetup command is even more basic because it doesn't even check if there is a setups environment with the given name which is done by the other commands.

3. Is the support for {} and [] in setup simply to maintain legacy support for {}, or are there reasons to choose one over the other? I do see consistently faster times with the curlies.

You can run Hans example with MkIV and the differences should be even bigger because the check for [] is slower here while in LMTX it's a engine feature. The main difference in LMTX is a extra expansion for \setup compared to \directsetup.

4. Are there operations that are supported in directsetup that are not supported in setup or fastsetup? Are there operations supported in fastsetup that are not supported in setup or directsetup?

There is no difference between \setup and \directsetup but \fastsetup should only be used when you can ensure the requested environment exists.

5. Is it fair to say that setup can do the most, directsetup a bit less, and fastsetup is the most restrictive? Except for the most performance-constrained documents, setup is a safe choice, but when constructing modules or performance tuning, the others might be tested?

As I already wrote before there is no difference between \setup and \directsetup. When you care about performance \directsetup is the wrong start because you won't notice a difference.

Wolfgang