Some functions in ggh4x are using extensions to the theme system. These extended theme argument are listed below, along with what elements they are expected to be, and in what function(s) they are used.
An element_line() used as the parent for the
nest_line argument in facet_nested() and facet_nested_wrap().
Inherits directly from the 'line' theme element.
An
element_line() used as the line to separate different layers of labels
in guide_axis_nested(). Inherits from the 'axis.ticks' theme element.
An element_text() used
to differentiate text higher in the hierarchy from the axis labels directly
next to the axis line in guide_axis_nested(). Inherits from the
'axis.text.x' and 'axis.text.y' theme elements respectively.
A rel() object used to set the size
of minor tick marks relative to the regular tick marks. This is used in the
guide_axis_minor() and guide_axis_logticks() functions. Defaults
to rel(2/3).
A rel() object used to set the size
of the smallest tick marks relative to regular tick marks. This is only
used in the guide_axis_logticks() function. Defaults to rel(1/3).