I guess the intent of the second one is to create a child for the currently active schema leaf (namespace) if such exists (?). Without better knowledge, something like the following would make this more intuitive (to me):

sibling:
tools.dendron.notes.demo.md -> create new journal note -> tools.dendron.notes.journal.2020-08-03.md

child:
tools.dendron.notes.demo.md -> create new journal note -> tools.dendron.notes.demo.journal.2020-08-03.md

root:
tools.dendron.remarks.md -> create new journal note -> journal.2020-08-03.md

schema:
tools.dendron.notes.demo.md -> create new journal note -> tools.dendron.journal.2020-08-03.md

in this example, the schema-option assumes that "tools" is defined in the schema, and it has set namespace to true.

Continuing on this, the term "namespace" is also somewhat hard to understand correctly. Elsewhere in the docs: "when a schema is a namespace, it can have arbitrary children. equivalent to cli.* glob pattern". What makes this difficult is that any node in the schema can anyway have arbitrary children, since "...you can create notes that don’t match any schema". Anyway, after spending some time on this, I think I now know how it works. Maybe formulating namespace something like this could help "making a schema node a namespace automatically brings its immediate children as part of the schema, even if they are not explicitly defined in the schema definition".