<th1>
  #
  # This is a "TH1 fragment" used to test the Tcl integration features of TH1.
  # The corresponding test file executes this file using the test-th-render
  # Fossil command.
  #
  proc doOut {msg} {puts $msg; puts \n}

  if {[tclInvoke set tcl_version] >= 8.6} {
    doOut [tclInvoke tailcall set x 1]
  } else {
    error "This test requires Tcl 8.6 or higher."
  }
</th1>