In-Portal is using CKEditor as it's WYSIWYG editor. It has bundled Content Templates Add-On (see http://ckeditor.com/addon/templates), however there no much documentation about how to use it.
By inspecting source code I've found it can be connected to In-Portal:
This add-on allows to add predefined code snippets into the page.
Solution
- enable "Content Templates" add-on in CKEditor
- developer must enable "Templates" button on CKEditor toolbar manually, when needed (not enabled by default because nobody wants to have default templates inserted)
- allow specifying template configuration in "templates.js" file, that is located in same folder as "style.css" and "styles.js" files