Fatal error

Hi,
you once gave me this code to add a slogan & a subslogan into the headarea of my website:
(You cant see it live cause i removed it again)

add_filter('avf_logo_subtext', 'kriesi_logo_addition');
function kriesi_logo_addition($sub)
{
	$sub .= "<div id='headText'>
					<a href='https://www.maskenzauber.com'><h1>Venezianische<span> Masken</span></h1></a>
					<span id='subslogan'>Handgefertigt in Berlin</span>
				</div>";
	$sub .= "<div id='headClaim'>
				<strong>Here comes</strong>
					another claim
				</div>";
	return $sub;
}

But this leads to a fatal error according W3C:

Element div not allowed as child of element span in this context. (Suppressing further errors from this subtree.)
From line 232, column 267; to line 232, column 285
‘subtext’><div id=’headText’>↩

Contexts in which element div may be used:
Where flow content is expected.
As a child of a dl element.
Content model for element span:

Followed by these errors:

Error: Start tag a seen but an element of the same type was already open.

From line 233, column 6; to line 233, column 39

xt’>↩ <h1>Ve

Error: End tag a violates nesting rules.

From line 233, column 6; to line 233, column 39

xt’>↩ <h1>Ve

Fatal Error: Cannot recover after last error. Any further errors will be ignored.

From line 233, column 6; to line 233, column 39

xt’>↩ <h1>Ve

Here is the complete output:

<div class='container av-logo-container'><div class='inner-container'><span class='logo'><a href='https://www.maskenzauber.com/'><img height="100" width="300" src='https://maskenzauber.com/graphic/logo.png' alt='Maskenzauber' title='' /><span class='subtext'><div id='headText'>
					<a href='https://www.maskenzauber.com'><h1>Venezianische<span> Masken</span></h1></a>
					<span id='subslogan'>Handgefertigt in Berlin</span>
				</div><div id='headClaim'>
				<strong>Here comes</strong>
					another claim.
				</div></span></a></span>

Maren