Created by labs(), ggtitle(), xlab(), ylab(); added with +.
Any field left NULL falls back to the default (for axes, the deparsed
aesthetic mapping).
Labels(
title = NULL,
subtitle = NULL,
caption = NULL,
tag = NULL,
x = NULL,
y = NULL,
color = NULL,
size = NULL,
fill = NULL
)An S7 object of class Labels; usually built by labs().