The placeholder attribute is used to add the print-me data to the page when print trigger and target will be added dynamically, for example: via AJAX or a Modal Window.
[print-me target="#print_me" placeholder="true"/]
This will not add the trigger to the page, just the targeting info for when the trigger is later displayed.
This is an example of a collapse element with an inline link.
[expand title="this is a test with a <a href='https://plugins.twinpictures.de'>link</a>"]here is some hidden content[/expand]
the key is to use double quotes to wrap the title attribute and single quotes for the html inside the double quotes.
this is a test with a link
here is some hidden content