dcl-command-regexp is a variable defined in `dcl-mode.el'.
Its value is

"^\\$\\(.*-[ ]*\\(!.*\\)*\n\\)*.*\\(\".*\\(\"\".*\\)*\"\\)*"

Regular expression describing a DCL command line.
A line starting with $, optionally followed by continuation lines,
followed by the end of the command line.
A continuation line is any characters followed by `-',
optionally followed by a comment, followed by a newline.

You can customize this variable.