Oh, it breaks if any of the elements consists of more than one character:

% perl -le 'print"@{[split//,join q(x),split/(?<=c)/,join(q(),qw(a b c
+ d c e foo f)),2]}"'
a b c x d c e f o o f
[download]

but single spaces are fine:

% perl -le 'print"@{[split//,join q(x),split/(?<=c)/,join(q(),qw(a b c
+ d c e),q( ),q(f)),2]}"'
a b c x d c e   f
[download]

To fix this, I guess one could do something like

perl -le 'print"@{[split/\0/,join qq(\0x),split/(?<=c)/,join(qq(0),qw(
+a b c d c e foo f)),2]}"'
a b c x d c e foo f
[download]