Allows an ERB template to be rendered in the context (binding) of an existing ERB template evaluation.
Overrides compiler startup to set the eoutvar to an empty string only if it isn't already set.
# File ruby-3.1.2/lib/rdoc/erb_partial.rb, line 12
def set_eoutvar compiler, eoutvar = '_erbout'
super
compiler.pre_cmd = ["#{eoutvar} ||= +''"]
end