It would be nice if the plugin can parse text based files (*.txt, *.html, *.xml, etc...), to retrieve the YVALUE to plot.

A typical usage would be for parsing file generated from other tools, for example, lcov generate the coverage info from gcov output, it would be nice to configure the plot plugin to parse the main page generated by lcov, and to plot the line coverage percentage with time.

I think this way the plot plugin would be more general and will still be backward compatible.