class Sass::SemiGlobalEnvironment

directives.
create new variables in the global scope. Useful for top-level control
An environment that can write to in-scope global variables, but doesn’t

def try_set_var(name, value) 

def try_set_var(name, value)
  @vars ||= {}
  if @vars.include?(name)
    @vars[name] = value
    true
  elsif @parent
    @parent.try_set_var(name, value)
  else
    false
  end
end