Capybara: How to define custom selectors?
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I often need to query for elements within the sidebar. However, the css selector that I have to use is temporary and pretty ugly:

    <div id="rt_mod_side_foo_body_bar">

I would like to abstract this so instead of writing:

    within '#rt_mod_side_foo_body_bar'

I can do:

    within :sidebar

How can this be accomplished with Capybara?