Function validate_scope_chain 

pub fn validate_scope_chain(
    token: &Token,
    data: &Everything,
    sc: &mut ScopeContext,
    qeq: bool,
) -> bool

Validate the left-hand part of a target = { target_scope } block.

The caller is expected to have done sc.open_builder() before calling and then do sc.close() after calling. Returns true iff validation was complete. qeq is true if the scope chain is to the left of a ?= operator.