Slots are pretty easy in Phlex. Have a look at the README in the repo I linked for an idea. I just create `with_column` or `with_header` methods that take a block and store it.

To create them declaratively (not needing to call them in a set order) you just create a module that defines `before_template` and calls `vanish`: https://www.phlex.fun/miscellaneous/v2-upgrade.html#removed-...