Now that a node can be in two separate docs, it's position must be encoded separately or we cannot have it positioned in two separate places in two documents.
Options:
Encode position in document node, i.e. the meta node.
Make the attribute names even uglier, encoding the document name in them, i.e.
layouts_doc_A_custom_y
where 'doc_A' is an attribute-name-validity-respecting encoding of the document name. (i.e. spaces and other whitespace and illegal chars to underscores).
Now that a node can be in two separate docs, it's position must be encoded separately or we cannot have it positioned in two separate places in two documents.
Options: