Interesting that both | and ^ were supported, but | took over and ^ is still unused by the shell.
I wonder if ^ was deprecated because of the likelihood it'd be commonly used at the start of a regexp for grep, but | used to provide alternatives in a regexp was probably much less frequently used and so having to quote is was less of a problem than for ^.
Also interesting that the v3 format had both input and output filters, which is just semantic repositioning of the commands.
