semantic tag for full page

[wb_user]

it support in layer and some objects
is that possible to i set that in one html page?
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page or content place holder

[Pablo]

You will need to set this option for each object individually, because there are multiple choices so you cannot set it it the same for all objects.

[wb_user]

You will need to set this option for each object individually, because there are multiple choices so you cannot set it it the same for all objects.

are this is good idea to add semantic tag in content place holder?

[Pablo]

A content place holder is not an element, it's a place holder which will be replaced with the actual content when you preview/publish the page.