The API index lists the nine types cl-harfbuzz now exports, and each
page that describes their values names them: direction, cluster-level
and buffer-flag on Shaping, font-source on Faces, glyph-index and
metric on Fonts and metrics, name-id and layout-table on OpenType
data, and color on Color glyphs. Installation says which names a
package that uses cl-harfbuzz together with cl-ft2, cl-svgread or
cl-harfbuzz/ffi must shadow.
