# Receive notification of the beginning of an element.
	#
	# The Parser will invoke this method at the beginning of every
	# element in the XML document; there will be a corresponding
	# `end_element` event for every startElement event
	# (even when the element is empty). All of the element's content will be
	# reported, in order, before the corresponding `end_element`
	# event.
	#
	# This event allows up to three name components for each
	# element:
	#
	# 1. the Namespace URI;
	# 2. the local name; and
	# 3. the qualified (prefixed) name.
	#
	# Any or all of these may be provided, depending on the
	# values of the `http://xml.org/sax/features/namespaces`
	# and the `http://xml.org/sax/features/namespace-prefixes`
	# properties:
	#
	# * the Namespace URI and local name are required when
	# the namespaces property is `true` (the default), and are
	# optional when the namespaces property is `false` (if one is
	# specified, both must be);
	# * the qualified name is required when the namespace-prefixes property
	# is `true`, and is optional when the namespace-prefixes property
	# is `false` (the default).
	#
	# Note that the attribute list provided will contain only
	# attributes with explicit values (specified or defaulted):
	# `#IMPLIED` attributes will be omitted. The attribute list
	# will contain attributes used for Namespace declarations
	# (`xmlns*` attributes) only if the
	# `http://xml.org/sax/features/namespace-prefixes`
	# property is true (it is `false` by default, and support for a
	# `true` value is optional).
	#
	# Parameters:
	#
	# * `uri`: Namespace URI, or the empty string if the
	# element has no Namespace URI or if Namespace
	# processing is not being performed.
	# * `localName`: local name (without prefix), or the
	# empty string if Namespace processing is not being
	# performed.
	# * `qname`: The qualified XML 1.0 name (with prefix), or the
	# empty string if qualified names are not available.
	# * `atts`: attributes attached to the element.
	#
	# SEE: `end_element`
	# SEE: `sax::Attributes`
	fun start_element(uri: String, local_name: String, qname: String,
			atts: Attributes) do end