An example of using matches to narrow a messy selection by using an unanchored pattern
to replace data with a substring.

-- rules --
data matches [a-zA-Z0-9_\-./@]+\.pdf
data set $0
plumb to edit

-- initial --
src: bash
dst: ad
wdir: /home/foo/bar
ndata: 48
data: $ zathura my-awesome-pdf.pdf some-other-pdf.pdf

-- processed --
src: bash
dst: ad
wdir: /home/foo/bar
ndata: 18
data: my-awesome-pdf.pdf
