sceadu-fæx

Shadow DOM Facsimile

There's a promising proposal that recognizes that the slot mechanism ShadowDOM provides is useful even outside the confines of style encapsulation.

sceadu-fæx (or alternatively shadow-fax) is a web component that provides limited support for slotting without using native ShadowDOM -- sticking to light children. It also does it outside the confines of a traditional web component, where the ShadowDOM is kinda/sorta nested in a kind of parent/child relationship. So this implementation is definitely not a drop-in "ShadowDOM slotting without ShadowDOM" replacement, as there are significant differences in behavior.

sceadu-fæx extends xtal-fragment, and thus inherits its basic syntax. xtal-fragment lacks ShadowDOM-lite slotting emulation, which is the value-add proposition sceadu-fæx provides.

Perhaps it is best to describe what sceadu-fæx does with an example:

<template id=my-field-category-holder>
<make-fieldset-expandable></make-fieldset-expandable>
<fieldset>
  <legend><slot-nik name=label>My {{nameOfCategory}}</slot-nik></legend>
  <slot-nik name=field-container></slot-nik>
</fieldset>
</template>

<sceadu-fæx from=my-field-category-holder>
    <templ-model name-of-category="First Category"></templ-model>
    <ref-to a=h3 slot=label></ref-to>
    <ref-to a=my-grid slot=field-container></ref-to>
    <ref-to a=my-chart slot=field-container></ref-to>
</sceadu-fæx>

generates:

<template id=my-field-category-holder>
...
</template>

<sceadu-fæx style=display:none from=my-field-category-holder>
    <templ-model name-of-category="First Category"></templ-model>
    <ref-to a=h3 slot=label></ref-to>
    <ref-to a=my-grid slot=field-container></ref-to>
    <ref-to a=my-chart slot=field-container></ref-to>
</sceadu-fæx>
<make-fieldset-expandable></make-fieldset-expandable>
<fieldset>
  <legend>
      <slot-nik name=label style=display:none></slot-nik>
      <h3 slot=label>My First Category</h3>
  </legend>
  <slot-nik name=field-container style=display:none></slot-nik>
  <my-grid slot=field-container></my-grid>
  <my-chart slot=field-container></my-chart>
</fieldset>

As we can see, sceadu-fæx works best in conjunction with web components slot-nik, which emulates slots, and ref-to, which creates references to live slotted elements (based on the a attribute).

NB: This component might not play well with other rendering libraries. For a rendering library to be compatible with this component, it must use the following API:

1. If the contents "grouped" by sceadu-fæx need to be moved to a new location in the DOM tree, this should be done via newDestination.appendChild($0.extractContents()) where $0 is the instance of sceadu-fæx.
2. The rendering library may need to skip over the owned siblings when updating the DOM, via $0.nextUngroupedSibling, where $0 is the instance of sceadu-fæx (unless the renderer is aware of the contents of the template sceadu-fæx is copying from).

What happens when the light children change?

1. If ref-to is removed, the element it created is removed.
2. If a ref-to element is added with a slot-nik attribute, it is appended to the grouped sibling managed for that slot.
3. Changes to the actual element must be done via refToElement.deref, if it exists.