This script:

# == +Test+ for RDoc::usage
#
# RDoc formats this as HTML without problems
# but dies when formatted with RDoc::usage

require 'rdoc/usage'
RDoc::usage

fails with the the following message:
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/inline.rb:23:in `as_string': 
undefined method `zero?' for nil:NilClass (NoMethodError)
        from /usr/lib/ruby/1.8/rdoc/markup/simple_markup/inline.rb:47:in 
`to_s'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb:167:in `join'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb:167:in 
`display_flow_item'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb:211:in `display_flow'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb:210:in `each'
        from /usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb:210:in `display_flow'
        from /usr/lib/ruby/1.8/rdoc/usage.rb:122:in `usage_no_exit'
        from /usr/lib/ruby/1.8/rdoc/usage.rb:93:in `usage'
        from ./rdoc_usage.rb:9

If I run rdoc to generate HTML, it works as expected.
RDoc::usage works if I remove the markup for "Test"
in the heading.
Is this an rdoc bug?

-- 
Stefan