Constructor.
The original HED string.
The nested list of parsed HED tags and groups.
All the column splices in the string at all levels.
The top-level definition tag groups in the string.
The original HED string.
The parsed substring data in unfiltered form.
The tag groups in the string (top-level).
All the tags in the string at all levels
The tags in the top-level tag groups in the string, split into arrays.
All the top-level tags in the string.
A parsed HED string.