Title of the Design
===================

<!-- Describe your change here.  This is purposefully freeform: we want
enough information to evaluate the design, but not so much that you're
annoyed by the overall design process and decide to bake cookies instead.
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## Example

<!-- Specify an example of how the user would use this.  It helps other
contributors get a feel for how this will look in real code, and provides
a good opportunity to evaluate the end-user feel of the code for yourself.

If you find yourself groaning at verbosity, copy-and-pasting a lot, or
writing a bunch of tiny helper functions, it's a good indication that you
might need to re-evaluate the user experience of your design.

This is also a good opportunity to stop and write a proof-of-concept, if
you haven't already, which should help catch practical nits with the
design. -->