(command.CommandList
  children: [
    (command.ShFunction
      name: usage
      body: 
        (BraceGroup
          left: <Id.Lit_LBrace '{'>
          children: [
            (C {<echo>} {(DQ <'Usage: hal-fdi-validate [-f dtd] file [file ...]'>)})
            (command.ControlFlow token:<Id.ControlFlow_Exit exit> arg_word:{<1>})
          ]
          redirects: []
          right: <Id.Lit_RBrace '}'>
        )
    )
    (command.If
      arms: [
        (if_arm
          cond: 
            (condition.Shell
              commands: [
                (command.Sentence
                  child: 
                    (C {<Id.Lit_LBracket '['>} {(DQ ($ Id.VSub_Number 1))} {<Id.Lit_Equals '='>} 
                      {(DQ <-f>)} {<Id.Lit_RBracket ']'>}
                    )
                  terminator: <Id.Op_Semi _>
                )
              ]
            )
          action: [
            (command.If
              arms: [
                (if_arm
                  cond: 
                    (condition.Shell
                      commands: [
                        (command.Sentence
                          child: 
                            (C {<Id.Lit_LBracket '['>} {(DQ <foo> ($ Id.VSub_Number 2))} 
                              {<Id.KW_Bang '!'> <Id.Lit_Equals '='>} {(DQ <foo>)} {<Id.Lit_RBracket ']'>}
                            )
                          terminator: <Id.Op_Semi _>
                        )
                      ]
                    )
                  action: [
                    (command.ShAssignment
                      pairs: [
                        (assign_pair
                          lhs: (sh_lhs_expr.Name left:<Id.Lit_VarLike 'DTD='> name:DTD)
                          op: assign_op.Equal
                          rhs: {(DQ ($ Id.VSub_Number 2))}
                          spids: [95]
                        )
                      ]
                      redirects: []
                    )
                    (C {<shift>} {<2>})
                  ]
                  spids: [72 92]
                )
              ]
              else_action: [(C {<usage>})]
              redirects: []
            )
          ]
          spids: [52 69]
        )
      ]
      else_action: [
        (command.ShAssignment
          pairs: [
            (assign_pair
              lhs: (sh_lhs_expr.Name left:<Id.Lit_VarLike 'DTD='> name:DTD)
              op: assign_op.Equal
              rhs: {(DQ <'/usr/share/lib/xml/dtd/fdi.dtd.1'>)}
              spids: [117]
            )
          ]
          redirects: []
        )
      ]
      redirects: []
    )
    (command.If
      arms: [
        (if_arm
          cond: 
            (condition.Shell
              commands: [
                (command.Sentence
                  child: 
                    (C {<Id.Lit_LBracket '['>} {($ Id.VSub_Pound '#')} {<-eq>} {<0>} 
                      {<Id.Lit_RBracket ']'>}
                    )
                  terminator: <Id.Op_Semi _>
                )
              ]
            )
          action: [(C {<usage>})]
          spids: [125 138]
        )
      ]
      else_action: []
      redirects: []
    )
    (C {<xmllint>} {<--noout>} {<--dtdvalid>} {($ Id.VSub_DollarName DTD)} {($ Id.VSub_Star '*')})
  ]
)