Meta tag 'there is no attribute “class” ' and 'there is no attribute “property” 'and other attribute error

Question

I tried to validate my website and I get the following error :

there is no attribute "class"

<aside class="left-off-canvas-menu">

element "aside" undefined

<aside class="left-off-canvas-menu">

there is no attribute "property"

<meta property="og:title" content="Growth Scorecard" />

document type does not allow element "div" here

…+' preptimeline timeline-portion" title="'+titles[parseInt(val)-1]+'"></div>');

How can I solve this error please suggest to me. I have less knowledge of XHTML. please let me know. why an error occurs on my website.

You can see validator's error report.

Answer 1

The elements and attributes you are using were introduced in HTML 5.

XHTML 1.0 Transitional is too old to support them.

Use HTML 5 instead. It better reflects what browsers actually support and what you are trying to do.