/* ════════════════════════════════════════════════════════════════════════

* isCustomElement(el)

* ------------------------------------------------------------------------

* Determines whether a given DOM element should be treated as an EHTML

* custom element.

*

* EHTML supports two kinds of custom elements:

*

* 1. Autonomous custom elements

* Defined directly by tag name:

* <e-json>, <e-html> etc.

*

* 2. Customized built-in custom elements

* Defined using the "is" attribute:

* <template is="e-wrapper">

* <form is="e-form">

* <select is="e-select">

*

* Detection rules:

*

* • If 'el' is not an Element → false

* • If tagName exists in customElements registry → true

* • If "is" attribute exists and its value is registered → true

* • Otherwise → false

*

* Notes:

* • This function does *not* check activation state; it only determines

* whether an element *represents* an EHTML custom element type.

* • Works reliably even on browsers that refuse to upgrade customized

* built-ins (notably iOS Safari).

* ════════════════════════════════════════════════════════════════════════ */

export default function isCustomElement(el) {

/* * Skip all non-element nodes (text, comments, fragments, etc.)

*/

if (!(el instanceof Element)) {

return false

}

/* * Autonomous custom elements:

* Their tag name is the registered custom element type.

*/

const tagName = el.tagName.toLowerCase()

if (customElements.get(tagName)) {

return true

}

/* * Customized built-in elements:

* They declare their custom element type via the "is" attribute.

*

* Example:

* <template is="e-wrapper">

* <form is="e-form">

*

* We check whether the "is" type exists in the customElements registry.

*/

const isAttr = el.getAttribute('is')

if (isAttr) {

const type = isAttr.toLowerCase()

if (customElements.get(type)) {

return true

}

}

/* * No matching custom element definition was found.

*/

return false

}