Most text editors support custom syntax highlighting and, sometimes, simple autocompletion. But, that's not enough for me :)
I'm looking for editor with autocompletion/tooltips for functions, similar to IntelliSense in Visual Studio.
For example, if my custom language has a standard function doSomething(what, when, where) and I constantly forget order of the parameters, I'd like my editor to be able to help me filling the params as soon as I type doSomething(, by for example displaying little tooltip doSomething(what, when, where).
It will be good enough if it worked with preconfigured functions only. I don't need it to autocomplete functions that are defined in the edited file.