Translate html attributes such as alt tilte using http API

Greetings,

I'm using translator http "Translate" API (GET).

When I translate this html: <div title="this is the title">this is the text</div>

Only the innerHtml gets translated, for example translating to spanish the result is:

<div title="this is the title">este es el texto</div>

I'm already setting contenttype=text/html, the result IS valid html, but title / alt are not translated.

I am doing something wrong or is this not supported by the Microsoft Translator.

Thanks in advance