For T94890, RESTBase needs the HTML offsets for top-level children of <body> so that those elements can be edited in isolation (in VE, mobile editing, etc.). It should be possible to gather these offsets relatively easily in the XMLSerialization code.
The proposal right now is to return a new json blob, data-section-offsets:
{
mwxxx: {
wt: [183,235],
html: [384,568]
},
....
}Alternatively, this info could be folded into a separate section_offsets object in data-parsoid, which would be documented as a public API.