The syntax of the oplot input is strict. Drawing commands, such as move, line or text may only be present inside an open object. If oplot discovers a syntax error, it simply stops, with an indication of which input line the error occured (usually, the next line is where the problem lies). However, the syntax is also simple, so hopefully it should be easy to debug input files. The oplot input syntax is very similar to the O graphics descriptor language, but not completely identical.