A <substep> element has the same structure as a <step>, except that it does not allow lists of choices or sub-steps within it, in order to prevent unlimited nesting of steps.
See appendix for information about this element in OASIS document type shells.
- topic/li task/substep
- Describes whether the current <step> or <substep> is optional or required. Output processors might highlight steps that are optional or required. Allowed values are "optional", "required", or -dita-use-conref-target.