Assemble of own packages in MODX EVO was possible long time ago ,from 1.0.4 version in folder install/assets/ files with .tpl extension was present — for creation of all MODX elements, and setup.data.sql, for creation of demo-content. MODX-STORE uses same structure of package
Package consist of 2 parts , “assets” and “install” folders and represent zip archive, which consider folder with package same as package name (or name can be random) and have 2 sub-folders:
assets – include all necessary files for work of yours elements, which necessary upload to assets folder, preserve standard structure of MODX folders.
install – holds assets folder, where all necessary elements gathered (files with .tpl extensions), and setup.data.sql file, for creating demo-content.
Fast installation consist in auto installation, which do not need unnecessary activity from user.
Extended installation allow to choose elements which user want to install. This option also allow to choose – do you want to install demo –content or no?
Type of installation depends on which type you choos type on upload of a new package. All elements, except packages are fast to install, and extended install uses for extended install.
I think that is better to see once then 10 times to read. On following refer you can study how to other packages assembled.