This module is written to be imported qualified. It defines the syntax for HTML-like values for use in Graphviz. Please note that these values are not really HTML, but the term "HTML" is used throughout as it is less cumbersome than "HTML-like". To be able to use this, the version of Graphviz must be at least 1.10. For more information, please see: http://graphviz.org/doc/info/shapes.html#html

The actual definition of the syntax specifies that these types must be valid XML syntax. As such, this assumed when printing and parsing, though the correct escape/descaping for ", &, < and > are automatically done when printing and parsing.

Differences from how Graphviz treats HTML-like values:

• Graphviz only specifies the above-listed characters must be escaped; however, internally it also escapes -, ' and multiple sequences of spaces. This library attempts to match this behaviour. Please let me know if this behaviour (especially about escaping multiple spaces) is unwanted.
• When parsing escaped HTML characters, numeric escapes are converted to the corresponding character as are the various characters listed above; all other escaped characters (apart from those listed above) are silently ignored and removed from the input (since technically these must be valid XML, which doesn't recognise as many named escape characters as does HTML).
• All whitespace read in is kept (even if Graphviz would ignore multiple whitespace characters); when printing them, however, they are replaced with non-breaking spaces. As such, if multiple literal whitespace characters are used in a sequence, then the result of parsing and then printing some Dot code will not be the same as the initial Dot code. Furthermore, all whitespace characters are printed as spaces.
• It is assumed that all parsed & values are the beginning of an XML escape sequence (which must finish with a ; character).
• There should be no pre-escaped characters in values; when printing, the & will get escaped without considering if that is an escaped character.