MetaMarker
WLJS
Wolfram Kernel
Execution environment
Notebook`Editor`Kernel`FrontSubmitService`MetaMarkers`
Context
MetaMarker[uid_String] _MetaMarker
an object used to mark frontend instances or select them and their contexts to be used later with FrontSubmit. One can think about if it assigns a given identifier to a group of expressions and saves their context of the evaluation.
Please, see an examples on FrontSubmit.