# Declare a Namespace prefix for this context.
	#
	# Parameters:
	#
	# * `prefix`: prefix to declare.
	# * `uri`: associated Namespace URI.
	#
	# SEE: `NamespaceSupport.declare_prefix`
	fun declare_prefix(prefix: String, uri: String) do
		assert legal_state: decls_ok else
			sys.stderr.write("Can't declare any more prefixes in this context.\n")
		end

		# Lazy processing...
		if not decl_seen then
			copy_tables
		end

		if "" == prefix then
			if "" == uri then
				default_ns = null
			else
				default_ns = uri
			end
		else if "" == uri then
			prefix_table.keys.remove(prefix)
		else
			prefix_table[prefix] = uri
		end
		declarations.push(prefix)
	end