Errors and warnings should include line number when possible

Error and warning messages (i.e. those produced by merror and mwarning) should include, when possible/applicable, the line number in the experiment XML of the component that produced the message. For example, if the user attempts to divide by zero, the associated error message should include the line number of the action that evaluated the offending expression.

Obviously, this will require that MWorks starts storing line numbers (possibly in the base Component class).