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HTML to XHTML Conversion

HTML follows a much "looser" set of rules than XHTML. For instance:

  • Optional Tags: You can omit closing tags like </li>, </p>, or even </html> and </body> and browsers will still render the page correctly.
  • Unquoted Attributes: HTML allows attributes without quotes if the value doesn’t contain spaces or special characters.
  • Case Insensitivity: Tags and attributes aren’t case-sensitive — <BODY> and <body> are treated the same.
  • "Tag Soup" Tolerance: Browsers use error-correcting algorithms to interpret malformed markup, often guessing what the author intended.

HTML to XHTML conversion may not "round trip". This means that if you apply ⎕XML to the XML result of the conversion, the resulting XHTML might not map identically to the original HTML.

Note

Be mindful that very messed up HTML may not be able to be parsed using either HTMLtoXHTML or HTMLtoXHTML2.
For instance '<a> <b </a>' will cause an error using either function.

HTMLtoXHTML

HTMLtoXHTML uses ⎕XML to parse HTML. When ⎕XML trips over a non-compliant element HTMLtoXHTML parses the error message and takes corrective measures and tries again. This continues until either the conversion completes or we encounter a situation that we couldn't handle. If you run into the latter, please log a GitHub issue.

Syntax xml ← {verbose} HTMLtoXHTML html
html A character vector representing the HTML to be converted
verbose (optional) A Boolean where a value of 1 indicates to display the error messages ⎕XML generates during processing
xml The ⎕XML 5-column matrix result representing the converted HTML
Examples 
       HTMLtoXHTML '<h2 id="foo">Hello</h2>'
┌─┬──┬─────┬────────┬─┐
│0│h2│Hello│┌──┬───┐│5│
│ │  │     ││id│foo││ │
│ │  │     │└──┴───┘│ │
└─┴──┴─────┴────────┴─┘

HTMLtoXHTML2

HTMLtoXHTML2 uses HTMLRenderer and the JavaScript XMLSerializer object to generate its XHTML result by:

  • creating an invisible HTMLRenderer with the supplied HTML argument
  • injecting a WebSocket to communicate back to APL
  • executing the JavaScript to parse the HTML
  • sending the result back to APL over the WebSocket
  • finally closing the HTMLRenderer
Syntax xml ← HTMLtoXHTML2 html
html A character vector representing the HTML to be converted
xml The ⎕XML 5-column matrix result representing the converted HTML
Examples 
       HTMLtoXHTML '<h2 id="foo">Hello</h2>'
┌─┬────┬─────┬────────────────────────────────────┬─┐
│0│html│     │┌─────┬────────────────────────────┐│3│
│ │    │     ││xmlns│http://www.w3.org/1999/xhtml││ │
│ │    │     │└─────┴────────────────────────────┘│ │
├─┼────┼─────┼────────────────────────────────────┼─┤
│1│head│     │                                    │1│
├─┼────┼─────┼────────────────────────────────────┼─┤
│1│body│     │                                    │3│
├─┼────┼─────┼────────────────────────────────────┼─┤
│2│h2  │Hello│┌──┬───┐                            │5│
│ │    │     ││id│foo│                            │ │
│ │    │     │└──┴───┘                            │ │
└─┴────┴─────┴────────────────────────────────────┴─┘

Differences between HTMLtoXHTML and HTMLtoXHTML2

As you can see from the examples above, HTMLtoXHTML and HTMLtoXHTML2 return somewhat different results. In general, the core HTML that is converted will be structurally the same.

  • HTMLtoXHTML2 requires HTMLRenderer which might not be installed or enabled.
  • HTMLtoXHTML2 adds <html>, <head> and <body> elements if they don't exist in the source HTML. This may produce different level numbers from HTMLtoXHTML.
  • HTMLtoXHTML and HTMLtoXHTML2 may return slightly different results when encountering "sloppy" or malformed HTML.
      XMLUtils.HTMLtoXHTML '<p><span>hello</p>there</span>world'
┌─┬────┬──────────┬───┬─┐
│0│p   │          │   │7│
├─┼────┼──────────┼───┼─┤
│1│span│hello     │   │5│
├─┼────┼──────────┼───┼─┤
│1│    │thereworld│   │4│
└─┴────┴──────────┴───┴─┘
      XMLUtils.HTMLtoXHTML2 '<p><span>hello</p>there</span>world'
┌─┬────┬──────────┬────────────────────────────────────┬─┐
│0│html│          │┌─────┬────────────────────────────┐│3│
│ │    │          ││xmlns│http://www.w3.org/1999/xhtml││ │
│ │    │          │└─────┴────────────────────────────┘│ │
├─┼────┼──────────┼────────────────────────────────────┼─┤
│1│head│          │                                    │1│
├─┼────┼──────────┼────────────────────────────────────┼─┤
│1│body│          │                                    │7│
├─┼────┼──────────┼────────────────────────────────────┼─┤
│2│p   │          │                                    │3│
├─┼────┼──────────┼────────────────────────────────────┼─┤
│3│span│hello     │                                    │5│
├─┼────┼──────────┼────────────────────────────────────┼─┤
│2│    │thereworld│                                    │4│
└─┴────┴──────────┴────────────────────────────────────┴─┘