Say what a lone address fragment does

The comment read as if every fragment were dropped. One with nothing before it
cannot be told apart from a helptags address, so it goes through as is.

autoload/fzf/vim.vim

@@ -554,10 +554,11 @@ endfunction
 " then not run.
 "
 " A pattern holding a tab reaches :BTags cut short, since it reads the field on
-" its own. Such a fragment matches the wrong line, so keep only the parts before
-" it, and accept an unterminated pattern alone, which is the whole address in a
-" helptags file. Running to the end of the line, it takes any '|' or ';' with it,
-" so it cannot chain a command either.
+" its own. Where earlier parts parsed, keep those and drop the fragment, since a
+" line number beats half a pattern. A fragment on its own is indistinguishable
+" from a helptags address such as '/*:Ag*', so it goes through unterminated, the
+" way a builtin tag jump takes the same field. Running to the end of the line, it
+" takes any '|' or ';' with it, so it cannot chain a command either.
 let s:tag_address_part = '\%(\d\+\|/\%(\\.\|[^/\\]\)*/\|?\%(\\.\|[^?\\]\)*?\)'
 let s:tag_address_open = '\%(/\%(\\.\|[^/\\]\)*\|?\%(\\.\|[^?\\]\)*\)'
 function! s:tag_address(rest)