Created for https://sourceforge.net/p/scintilla/feature-requests/1341/

DTD test files:
https://www.w3.org/TR/xml11/#prod-notes contains
https://www.w3.org/2002/xmlspec/dtd/2.10/xmlspec.dtd

https://www.w3.org/TR/html4/sgml/intro.html contains
https://www.w3.org/TR/html4/strict.dtd and https://www.w3.org/TR/html4/loose.dtd

https://www.w3.org/TR/SVG11/svgdtd.html#Introduction contains
https://www.w3.org/Graphics/SVG/1.1/DTD/svg11-flat-20110816.dtd

XML test files from https://www.w3.org/XML/Test/
https://www.w3.org/XML/Test/xmlts20130923.zip

xmlts20130923\xmlconf\sun\valid\pe03.xml

<!DOCTYPE root [
<!ELEMENT root (p)>
<!ELEMENT p (#PCDATA)>
<!-- Example 1 from XML spec 1.0 Appendix D -->
<!ENTITY example "<p>An ampersand (&#38;#38;) may be escaped
numerically (&#38;#38;#38) or with a general entity (&amp;amp;).</p>" >
]>
<root>&example;</root>

Here are three issues:

1. Don't terminate SGML when > is inside quoted string (as shown in above XML).
2. Color [ and ] as same style to make brace matching work.
3. Nested conational section or sub-section <![xxx[ ... ]]>.