The OpenDocument (ODT) templates are processed by (a forked version of) odf-report. The "odf-report wiki":
The templates use named sections, named tables, and variables. It is recommended to create and update the templates with LibreOffice. They need to be in 'ODT' format.
To create a section, use the Insert|Sections menu item.
To see which section a location in the document belongs to, put your cursor at the location, and then look in the status bar. For example, this document has 2 sections. The second section is called 'test':
To edit the name of the current section, use the Format|Sections menu.
Each template type has its own set of named sections that may be present in a template.
To set or update the name of a table, just right click it and choose 'Table Properties'.
Each template type has its own set of named tables that may be present in a template.
The templates make use of variables, which are written entirely in capitals by convention, and surrounded by square brackets. For example: [SALUTATION]. Variables may be styled in arbitrary ways (e.g. bold text, etc) and the style will be retained when they are substituted with values. Each template type has its own set of supported variables.