Kirby tools and helpers only working in short echo tags?

I am working within a template, and want to use the Html::Iframe helper, or the Html::email helper, etc.

However, I found, that

	Html::email('', 'Contact us - long PHP Tag') 

produces absolutely no output, while

<?= Html::email('', 'Contact us - short PHP echo Tag') ?>

produces the email link as wanted. Why is this?

I found some discussions like Using Html::iframe Tool
they all use the short echo tags.

Inside a short echo tag, I can’t make use of variables and longer PHP code.

<?= is a shortcut for <?php echo, hence everything which would be valid for the echo construct is valid for the short open tag as well, and everything which is not valid is not. See the PHP docs.

Ok I understand. All the Html:: functions and helpers do nothing but returnig a string. So I have to echo that string to get it in my HTML output.
It would be nice to have that information in the docs, or at least a little piece of example code.

Actually it is in the documentation which says “Return type: String”, and the fact that you have to echo or print a string to get it into the output is basic PHP knowledge, or, in other words, you should not expect to get any output from <?php "Hello world!"; ?>.