The glyph is an artifact: pagination, layout or background content, not the document's real content. It is inside a
marked-content sequence tagged Artifact, or, on a tagged page read in structure order, under an Artifact
structure element or not in the structure tree. Artifacts are extracted only when
IncludeArtifacts asks for them.
Artifact = 4
ISO 32000-2 §14.8.2.2.