html escape source text for clipboard copy (#248)

Author: andreer

src/mkdocs_jupyter/nbconvert2.py

@@ -303,7 +303,8 @@ def custom_highlight_code(source, language=None, metadata=None):
         formatter = HtmlFormatter(cssclass=classes)
         output = _pygments_highlight(source, formatter, language, metadata)
 
-        clipboard_copy_txt = f"""<div id="cell-{cell_id}" class="clipboard-copy-txt">{source}</div>
+        escaped = mistune.escape(source)
+        clipboard_copy_txt = f"""<div id="cell-{cell_id}" class="clipboard-copy-txt">{escaped}</div>
         """
         return output + clipboard_copy_txt