Okteta grammar file

Okteta grammar files are used by Okteta, an open source hex editor by the KDE project. See https://www.kde.org/applications/utilities/okteta/

There are two types:
 * XML driven grammar files
 * Javascript driven grammar files

The documentation of the grammars is not very well and could be found under https://userbase.kde.org/Okteta/Writing_structure_definitions