Internal Functions
The different internal variables and functions offered by Templater are available under different modules, to sort them. The existing internal modules are:
- App module: 
tp.app - Config module: 
tp.config - Date module: 
tp.date - File module: 
tp.file - Frontmatter module: 
tp.frontmatter - Hooks module: 
tp.hooks - Obsidian module: 
tp.obsidian - System module: 
tp.system - Web module: 
tp.web 
If you understood the object hierarchy correctly, this means that a typical internal function call looks like this:  <% tp.<module_name>.<internal_function_name> %>
Contribution
I invite everyone to contribute to this plugin development by adding new internal functions. More information here.