The HTMLTidy library

// There actually is a library for tidying HTML into XHTML called HTMLTidy
// See http://www.html-tidy.org/
// HTMLTidy is actually a great tool for dealing with 1990s-era tag soup
// HTML, I highly recommend it.

// This isn't the API for Tidy, but let's assume it's a C library returning
// errno domained error codes. out must be freed with free() after use.
extern "C" int tidy_html(char **out, size_t *outlen, const char *in, size_t inlen);