Parameter Description: Show Source
If TRUE, the parameter names of the object will
be printed which were used to create the plot; that may be, e.g.,
useful to check the values or to create own plots with the base R plot function.
Alternatively showSource can be defined as one of the following character values:
"commands": returns a character vector with plot commands
"axes": returns a list with the axes definitions
"test": all plot commands will be validated with eval(parse()) and
returned as character vector (function does not stop if an error occurs)
"validate": all plot commands will be validated with eval(parse()) and
returned as character vector (function stops if an error occurs)
Note: no plot object will be returned if showSource is a character.