Function: `XMLChildPos`

Gets the position of a child element within an XML document object.

The position, in an XmlChildren array, of the Nth child that has the specified name.

Method Signature

XMLChildPos(elem=[XML], childname=[string], n=[integer])

Argument	Type	Required	Description
`elem`	`XML`	`true`	The XML DOM object.
`childname`	`string`	`true`	The name of the child element.
`n`	`integer`	`true`	The position of the child element. 1-based.