Is your feature request related to a problem? Please describe.

I believe the expected behaviour for parameter completion is a bit inconsistent (presumably for good reasons), and it might be helpful to have some documentation to refer to.

To describe what I am seeing, if I make a class with two functions that have optional parameters (one named the other positional) and a pair of classes with constructors in the same pattern:

For the function with optional positional parameters, the autocomplete gives one relevant option which adds placeholders for the parameters:

For the function with named positional parameters, the autocomplete gives one relevant option which does not add placeholders for the parameters:

In the case of constructor functions, two relevant options appear - with and without (...):

Selecting the (...) option gives, in the case of optional named parameters, no placeholders:

Whereas if I select the option without (...) I get just the class name:

And if I then open the bracket, ie. hit '(' I get prompts for the parameters and a super helpful popover:

The constructor function for optional positional parameters follows the same pattern:

Describe the solution you'd like

The main thing that gets me is that I forget what to expect, eg. I select the (...) option in a constructor expecting placeholders because of the ... but get no placeholders and can't use Cmd . to get them and then can't remember if that's expected behaviour and have to go looking (which is all OK imo, but I figured it would be helpful if there were a reasonably obvious docs page that describes what to expect).

Describe alternatives you've considered

Additional context