This is the default implementation of the mixin parser.
Similar to mixin functions found in CSS pre-processors like SASS, this element will interpolate the inner markup of another element that it is linked to into its parent's body where the <mixin> tag is located.
The 'link' attribute must be set with the ID of the element to mix-in, or alternatively a valueless attribute with the '&' modifier.
Note only the inner tags of a linked element will be imported. This means text embedded directly into the linked element will not be included.
parser : 'mixin'
<template id='terms-template' >
<tag>Tag A</tag>
<tag>Tag B</tag>
<category>Example</category>
</template>
<post>
<title>Post A</title>
<mixin link='terms-template' />
</post>
<post>
<title>Post B</title>
<mixin &terms-template />
</post>