The SCITE editor that the MAXScript editor is built on supports autocomplete, which you can enable for recognized MAXScript.
NEW in 3ds Max 2020.1 Update: 3ds Max generates an API keyword list automatically to support MAXScript autocomplete. In previous versions, users need to generate this list themselves, save it to a file, and add an entry for it in the MAXScript Editor configuration file.
The configuration for autocomplete is located in the MAXScript Editor and MAXScript properties files.
In MXS_Editor.properties:
#autocomplete autocompleteword.automatic=1 autocomplete.choose.single=0
In MAXScript.properties:
#autocomplete autocomplete.MAXScript.ignorecase=1 autocomplete.MAXScript.start.characters=$(chars.alpha)$(chars.numeric)_#. autocomplete.MAXScript.useautogeneratedapi=1
To disable autocomplete, change autocomplete.MAXScript.useautogeneratedapi to 0.
You can generate the API list yourself using the generateAPIList() function:
ss = stringstream "" generateAPIList ss
For more information about these and other properties, see MaxScript Editor Properties File Settings and MAXScript-Specific Language Settings.