The character that is used to replace colons in element names. Used when constructing the names of definitions used to represent the element and attribute list declarations in the DTD. Trang generates a definition for each element declaration and attlist declaration in the DTD. The definition name is based on the element name. In RELAX NG, the definition names cannot contain colons; colons are allowed in element names in DTDs. Trang first tries to use the element names without prefixes. If this results in a conflict, Trang replaces the colon with the chars specified. If no chars is specified, a period is used.