Specifies the location where any child elements of the bound element are placed in the generated content.
Normally, if the element bound to has its own content, the anonymous content is not generated. However, with a children element, you can merge the content from the XUL element and the XBL content.
If the children tag contains content itself, that content will become the default content. If the element the binding is attached to contains content, the default content will be ignored. If the element does not contain content, the default content will be added.
Type: element id, must be unique in the window
A unique identifier so that you can identify the children with. You can use this as a parameter to getElementById and other DOM functions and to reference the element in style sheets.
Should be set to a tag name which acts as a filter for the XUL's content. Any tags that match the value of the includes attribute are placed at the location of the children element.