DTDs must declare the qualified names
<!ELEMENT svg:text (#PCDATA)>
If the prefix changes, the DTD needs to change to.
Parameter entity references can help when the prefix changes or is removed:
<!ENTITY % mathml-colon      ''>
<!ENTITY % mathml-prefix     ''>
<!ENTITY % mathml-exp        '%mathml-prefix;%mathml-colon;exp' >
<!ENTITY % mathml-abs        '%mathml-prefix;%mathml-colon;abs' >
<!ENTITY % mathml-arg        '%mathml-prefix;%mathml-colon;arg' >
<!ENTITY % mathml-real       '%mathml-prefix;%mathml-colon;real' >
<!ENTITY % mathml-imaginary  '%mathml-prefix;%mathml-colon;imaginary' >