HTML strings rejected

[PlanetEarthSoftware]

Dot allows html rather than text labels, delimited by angle brackets, e.g:

digraph D {

  node [shape=plaintext]

  FOO [ label = <The <font color='red'><b>foo</b></font>,<br/> the <font point-size='20'>bar</font> and<br/> the <i>baz</i>> ];

  FOO -> {BAR, BAZ};

}

HTML node label.dot.zip

This would be tricky to add and maintain backwards compatibility, we need to know whether the string was a normal string/"quoted string" or an .
Idea 1. Store the html string with the normal strings but have a method on Edge isHtml(string) that checks if the string was an html string, stored, possibly if F# supports it, a new HashMap(ReferenceEqualityComparer.Instance) where the string is matched by reference equals, checking it is the same string, rather than a string with the same value.

Idea 2. (not backwards compatible) store a DotString or a HtmlString both derived from DotValue so the reader can check which type of string it is. HtmlString could have a method getString() to extract just the text and convert
to '\n'.

[PlanetEarthSoftware]

One can not derived a class from string as .net string is sealed.