The SCITE editor that the MAXScript editor is built on supports autocomplete, which you can enable for recognized MAXScript. To enable autocomplete, you need an .API file that contains all MAXScript function names, and then set the appropriate autocomplete settings in the user properties file.
To generate an API file:
#autocomplete autocompleteword.automatic=1 autocomplete.choose.single=0 autocomplete.MAXScript.ignorecase=1 autocomplete.MAXScript.start.characters=$(chars.alpha)$(chars.numeric)_#. api.$(file.patterns.MAXScript)=<path_to_api_file>
Note: set the <path_to_api_file> to the fully qualified filename of the file you saved in the first step.
For more information about these and other user properties, see MaxScript Editor Properties File Settings.