FontSpec
data class FontSpec(val family: FontFamily, val bold: Boolean, val italic: Boolean, val name: String = "")
Platform-neutral descriptor for picking a substitute system font when a document font ships no embedded outlines (e.g. the PDF Standard-14, or a CSS font with no @font-face file). Render backends map family + bold + italic to a host typeface. No PDF (or other format) types cross the canvas seam, so every document handler (PDF, EPUB, ...) feeds the same FontSpec.