/usr/share/fish/completions/seq.fish is in fish-common 2.2.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | complete -c seq -s f -l format -d 'Use printf style floating-point FORMAT'
complete -c seq -s s -l separator -d 'Use STRING to separate numbers'
complete -c seq -s w -l equal-width -d 'Equalize width with leading zeroes'
complete -c seq -l help -d 'Display this help'
complete -c seq -l version -d 'Output version information'
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