Marked Content Sequences

Marked content sequences (MCS) are foundational to PDF structure. They use content stream operators (BMC, BDC, EMC) to identify portions of content with a tag and optional property list. MCS tags are distinct from structure element types (often called "tags" in Tagged PDF)—they operate at the content stream level. Understanding MCS tags is essential for creating accessible and well-structured PDFs.

Marked Content Operators

According to ISO 32000-2:2020, Section 14.6, marked content designates sequences of graphics objects in a content stream. Each sequence is bounded by a begin operator and the EMC (End Marked-content) operator.

The sequence operators are: BMC (Begin Marked-content) for sequences with a tag only; BDC (Begin Marked-content with properties) for sequences with a tag and an associated property list; and EMC (End Marked-content) to terminate any sequence.

Property lists provide additional information for a marked-content sequence. They can be specified as inline dictionaries or as name objects in the Properties subdictionary of the current resource dictionary. Marked-content points (MP, DP) are not used in Tagged PDF.

MCS Tags

The following marked content tags are defined in PDF and play important roles in Tagged PDF, accessibility, and document structure. Each tag is used with BDC and a property list (except where noted).