if doc.Links[key] != nil {
				return nil, fmt.Errorf("duplicate link reference %q; second in %s", key, filename)
			}
			doc.Links[key] = link
		}
	}
	// Remove headings with empty contents.
	doc.Blocks = removeEmptySections(doc.Blocks)
	if len(doc.Blocks) > 0 && len(doc.Links) > 0 {
		// Add a blank line to separate the links.
		lastPos := lastBlock(doc).Pos()
		lastPos.StartLine += 2

		The version of the installed Go tree, as reported by runtime.Version.
	`,
}

var HelpFileType = &base.Command{
	UsageLine: "filetype",
	Short:     "file types",
	Long: `
The go command examines the contents of a restricted set of files
in each directory. It identifies which files to examine based on
the extension of the file name. These extensions are:

	.go
		Go source files.
	.c, .h
		C source files.

	}
	sort.Slice(sortedFiles, func(i, j int) bool { return sortedFiles[i].Name() < sortedFiles[j].Name() })
	return sortedFiles, nil
}

// OverlayPath returns the path to the overlaid contents of the
// file, the empty string if the overlay deletes the file, or path
// itself if the file is not in the overlay, the file is a directory
// in the overlay, or there is no overlay.