# Declare a Namespace prefix.
	#
	# All prefixes must be declared before they are referenced.
	# For example, a SAX driver (parser)
	# would scan an element's attributes
	# in two passes: first for namespace declarations,
	# then a second pass using `process_name` to
	# interpret prefixes against (potentially redefined) prefixes.
	#
	# This method declares a prefix in the current Namespace
	# context; the prefix will remain in force until this context
	# is popped, unless it is shadowed in a descendant context.
	#
	# To declare the default element Namespace, use the empty string as
	# the prefix.
	#
	# Note that you must *not* declare a prefix after
	# you've pushed and popped another Namespace context, or
	# treated the declarations phase as complete by processing
	# a prefixed name.
	#
	# Note that there is an asymmetry in this library:
	# `prefix` will not return the `""` prefix,
	# even if you have declared a default element namespace.
	# To check for a default namespace,
	# you have to look it up explicitly using `uri`.
	# This asymmetry exists to make it easier to look up prefixes
	# for attribute names, where the default prefix is not allowed.
	#
	# Parameters:
	#
	# * `prefix`: prefix to declare, or the empty string to
	# indicate the default element namespace. This may never have
	# the value `xml` or `xmlns`.
	# * `uri`: The Namespace URI to associate with the prefix.
	#
	#
	# Returns:
	#
	# `true` if the prefix and the URI are legal, `false` otherwise.
	#
	# SEE: `process_name`
	#
	# SEE: `uri`
	#
	# SEE: `prefix`
	fun declare_prefix(prefix: String, uri: String): Bool do
		if prefix == "xml" or prefix == "xmlns" or
					uri == xmlns or uri == nsdecl then
			return false
		else
			current_context.declare_prefix(prefix, uri)
			return true
		end
	end