Create a sample HTML select of taxonomy terms I created a custom form in a custom module. (in a class that extends FormBase)
I want to add a (very) simple html select element, this select must contains all taxonomy elements of a specific vocabulary, like this, where the integers are the taxonomy term IDs.

&lt;select id="...&gt;
    &lt;option value="4"&gt;tutu&lt;/option&gt;
    &lt;option value="15"&gt;toto&lt;/option&gt;
    &lt;option value="61"&gt;tata&lt;/option&gt;
    ...
    &lt;option value="48"&gt;titi&lt;/option&gt;
&lt;/select&gt;


How can I create this &lt;select&gt; tag using the taxonomy term ID and the taxonomy term name? The users would not see the taxonomy term ID, but only the taxonomy term name.

With a vocabulary name, how can I generate the good structure (an array?) that allows me create the &lt;select&gt; tag?
You will need to get your terms (with a query or load the vocab), loop over them and create an array of term tid and term label. Set that array as the #options property on the select field in your form code.