Distinguish between data and metadata lines

[dwhieb]

Data lines are the ones that must follow a schema or have it explicitly specified with slash codes. If one data line has a slash code, all of them must.

Metadata lines do not have to follow any particular schema. If they have a slash code, it does not force other lines to have them.

You need to get the terminology here right, because you also have a metadata line (#). Perhaps rename the metadata line to info or title or header.