The attributes of the branches (often two) of the dendrogram's root
Arguments
dend
dendrogram object
the_attr
the attribute to get from the branches (for example "height")
warn
logical (default from dendextend_options("warn") is FALSE).
Set if warning are to be issued, it is safer to keep this at TRUE,
but for keeping the noise down, the default is FALSE.
Should a warning be printed when
the function is used on an object which is NOT a dendrogram.