for 2016+ see: http://undocumentedmatlab.com/blog/user-defined-tab-completions-take-2 Create local :
functionSignatures.json
For 2015 and below : http://undocumentedmatlab.com/blog/setting-desktop-tab-completions
Edit
ls (fullfile(matlabroot,'toolbox/local/TC.xml'))
edit(fullfile(matlabroot,'toolbox/local/TC.xml'))