list with two ites. Component "defined" is a boolean that indicates
whether the property is defined in the style. Component "value" gives
the actual value associated to the property.
# NOT RUN {style1 <- Rcss(text="points { cex: 2; }")
# cex is defined, col is not definedRcssProperty("points", "cex", Rcss=style1)
RcssProperty("points", "col", Rcss=style1)
# }