Cannot add custom data- attributes using MarkdownExtra

Test instructions 1) Login as a user who has page editing permissions. 2) In user preferences change editor to PlainText Area. 3) In a course create a new activity of "Text and media area" or "Page" in an arbitrary section. 4) Below the textfield of "Page content" change the selection to "Markdown format" and paste this markdown code: That's some text with a footnote. [^1] The note must appear at the end of the page. Here comes some code: ``` {.someclass lang=en data-foo=bar } def somecode():     print("Hello World") somecode() ``` And here some other code: ``` {.otherclass lang=se data-foo=bas } <script>     alert('horray'); </script> ``` And finally here we try to use some XSS in the code attributes: ``` {.otherclass lang=xss data-proc=alert('ups xss alarm' } import os; if { }main{ } :     print(os.path()) ``` This is the end of the text. [^1] : And that's the footnote.     That's the second paragraph.   5) Save and display. What is expected: 1) When you see the rendered result it should look very similar to the screenshot 2) Open the source code of the page (search for "hello" to get at the correct position), the three <code> elements should look like:   <pre><code class="someclass" lang="en" data-foo="bar">def somecode():     print("Hello World") somecode() </code></pre> <p>And here some other code:</p> <pre><code class="otherclass" lang="se" data-foo="bas"><script> alert('horray'); </script> </code></pre> <p>And finally here we try to use some XSS in the code attributes: <code> {{{} {.otherclass lang=xss data-proc=alert('ups xss alarm'} {}}} import os; if { } { }main__: print(os.path())</code> Note that the first two <code> elements contain the attributes that were given in the markuptext while the latter is some invalid markup and is not rendered correctly (but also no XSS alert etc. pops up).