Currently the XmlSerializer does not escapes the '>' characters so a string like this:
<x id="START_ITALIC_TEXT" ctype="x-i" equiv-text="&lt;i&gt;"/>
becomes
<x id="START_ITALIC_TEXT" ctype="x-i" equiv-text="&lt;i>"/>

This could easily be fixed by changing line 164 and 168 to include the '>' character

this:
return buf.push(' ', attrNode.name, '="', attrNode.value.replace(/[<&"]/g, this._xmlEncoder), '"');
becomes:
return buf.push(' ', attrNode.name, '="', attrNode.value.replace(/[<>&"]/g, this._xmlEncoder), '"');

same with line 168:
return buf.push(textNode.data.replace(/[<&]/g, this._xmlEncoder));
becomes:
return buf.push(textNode.data.replace(/[<>&]/g, this._xmlEncoder));

Since the change is so small did not feel like creating a pull request. However if you prefer a pull request I will be glad to create one