According to the HTML spec, only metadata content is allowed within the <head> element. If a custom element is encountered in the head, the HTML parser will close the document head from that point and add the rest to the document body. This means that if specific meta tags need to be present in the head, they cannot be replaced with a single custom element.
It is possible to put any element in the <head> of a document, but the browser will move it and all following elements to the <body>. Therefore, it is recommended to look for ways of abstracting and customizing tags at the HTML templating level.
Here's an example that demonstrates what happens when a custom element is placed in the <head>:
<html>
<head>
<script>
customElements.define("in-head", class extends HTMLElement {
connectedCallback() {
console.log(this.nodeName, "in:", this.parentNode);
}
});
</script>
<in-head></in-head>
<title>HELLO!</title>
<style>
body {
background: green;
}
</style>
<script>
console.log("End of head", document.body.children);
</script>
</head>
<body>
</body>
</html>When this code is run, the browser will move the <in-head> element and all following elements to the <body>, and the output in the console will be:
[in-head] in: body
This demonstrates that the custom element was moved to the body, and the console.log statement inside the <script> tag at the end of the head was executed after the custom element was moved.
Note that running the above snippet in a code snippet tool may produce different results, as the tool may add additional elements or modify the HTML structure.