allow to push attribute's diff from above about fmf HOT 2 OPEN

Just an obvious note: By solely using merging in children nodes (everywhere require+) you can achieve desired effect right now.
However with this new merging prefix one will be unable to override parent's attribute.

from fmf.

After some thinking I must say that if this is implemented it should be done on tmt side.
Simply +require would be treated as any other attribute (redefining, adding, deducting works as normally).
Just tmt would merge +require and require into a final require.
The workaround with using require+ everywhere is also possible it is just not that convenient.

from fmf.