beginner question regarding config.in syntax

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Hello all,
what files are processed with this rules? (target/dreamcast/config.in):

pkgfilter sed '

# mangle all packages to only build them in the cross stage (1)
s,^. \(.\)[^ ]*,X \11--------,;

# select some packages (and repositories) explicitely

/ 00-dirtree /          { p; d; };
/ linux-header /        { p; d; };
/ binutils /            { s,^. [^ ]*,X 0---------,; p; d; }
/ gcc /                 { s,^. [^ ]*,X 0---------,; p; d; }

/ uclibc /              { p; d; };
/ linux26sh /           { p; d; };

/ minit /               { p; d; };
/ fgetty /              { p; d; };

/ libowfat /            { p; d; };
/ busybox /             { p; d; };

/ zlib /                { p; d; };

/ ncurses /             { p; d; };

# / iptables /          { p; d; };
/ dropbear /            { p; d; };
/ rsync /               { p; d; };

# / gpm /                       { p; d; };

/ strace /              { p; d; };
# disable the rest
/.*/                    { s/^X /O / ; p; d; };'

Sorry for this beginner question, but i don't undestand the build proccess completely.

best regards,
flo