One bit's source slice within a bitmark document (from splitBits).
The bit's UTF-8 byte range; these tile the document (for chunking).
The bit's text, trailing whitespace trimmed.
Where source starts in the input, in positionEncoding units: input.slice(start, end) === source (UTF-16, the default).
source
positionEncoding
input.slice(start, end) === source
One bit's source slice within a bitmark document (from splitBits).