Error validation metadata

Hi,
Right before closing footer for all posts is inserted metadata but if you pass the w3c validator throws the error: “Element meta is missing required attribute content”
Seems that the content attribute is required if the meta element has an itemprop attribute

From Stackoverflow:

From WHATWG HTML and also HTML 5.1 (W3C Working Draft): “If […] itemprop is specified, then the content attribute must also be specified.”
From the old Microdata (W3C Note): “If a meta element has an itemprop attribute, […] the content attribute must be present.”

<span style="display: none;" itemprop="author" itemscope itemtype="https://schema.org/Person"><meta itemprop="name" content="xxx"></span><meta itemprop="datePublished" content="xxx"><meta itemprop="dateModified" content="xxx"><strong><meta itemscope itemprop="mainEntityOfPage" itemType="https://schema.org/WebPage" itemid="xxx"/></strong><span style="display: none;" itemprop="publisher" itemscope itemtype="https://schema.org/Organization"><span style="display: none;" itemprop="logo" itemscope itemtype="https://schema.org/ImageObject"><meta itemprop="url" content="xxx"></span><meta itemprop="name" content="xxx"></span><meta itemprop="headline " content="xxx"><span style="display: none;" itemprop="image" itemscope itemtype="https://schema.org/ImageObject"><meta itemprop="url" content="xxx"><meta itemprop="width" content="696"><meta itemprop="height" content="604"></span>

Any advice to solve it?

Here a capture with same error from Newspaper demo:

• This topic was modified 9 years by nairolf.