def single_line_rule_set?(rule)
      rule.children.all? { |child| child.line == rule.source_range.end_pos.line }
    end
def single_line_rule_set?(rule)
      rule.children.all? { |child| child.line == rule.source_range.end_pos.line }
    end
Return whether this rule set occupies a single line.

 Note that this allows:
   a,
   b,
   i { margin: 0; padding: 0; }

 and:

   p { margin: 0; padding: 0; }

 In other words, the line of the opening curly brace is the line that the
 rule set is considered to occupy.