The PangoRenderComponent enum (since pango 1.58) has 2 enumerators with the same value.
PANGO_RENDER_COMPONENT_BACKGROUND = 1 << 3,
PANGO_RENDER_COMPONENT_UNDERLINE = 1 << 3,
It looks strange. If it’s deliberate, it would be fine to say so in the documentation.
Similar to the documentation of PANGO_FONT_MASK_WIDTH, which is identical to PANGO_FONT_MASK_STRETCH.
* This is an alias for [flags@Pango.FontMask.STRETCH].