# File lib/asciidoctor/substituters.rb, line 786
  def resolve_subs(subs)
    candidates = subs.split(',').map {|sub| sub.strip.to_sym}
    resolved = candidates & SUB_OPTIONS 
    if (invalid = candidates - resolved).size > 0
      puts "asciidoctor: WARNING: invalid passthrough macro substitution operation#{invalid.size > 1 ? 's' : ''}: #{invalid * ', '}"
    end 
    resolved
  end