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+#    interface_definition.rnc: VyConf reference tree XML grammar
+#
+#    Copyright (C) 2014. 2017 VyOS maintainers and contributors <maintainers@vyos.net>
+#
+#    This library is free software; you can redistribute it and/or
+#    modify it under the terms of the GNU Lesser General Public
+#    License as published by the Free Software Foundation; either
+#    version 2.1 of the License, or (at your option) any later version.
+#
+#    This library is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+#    Lesser General Public License for more details.
+#
+#    You should have received a copy of the GNU Lesser General Public
+#    License along with this library; if not, write to the Free Software
+#    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
+#    USA
+
+# The language of this file is compact form RELAX-NG
+# http://relaxng.org/compact-tutorial-20030326.htm
+# (unless converted to XML, then just RELAX-NG :)
+
+# Interface definition starts with interfaceDefinition tag that may contain node tags
+start = element interfaceDefinition
+{
+    node*
+}
+
+# node tag may contain node, leafNode, or tagNode tags
+# Those are intermediate configuration nodes that may only contain
+# other nodes and must not have values
+node = element node
+{
+    (ownerAttr? & nodeNameAttr),
+    (properties? & children? & command?)
+}
+
+# Tag nodes are containers for nodes without predefined names, like network interfaces
+# or user names (e.g. "interfaces ethernet eth0" or "user jrandomhacker")
+# Tag nodes may contain node and leafNode elements, and also nameConstraint tags
+# They must not contain other tag nodes
+tagNode = element tagNode
+{
+    (ownerAttr? & nodeNameAttr),
+    (properties? & children & command?)
+}
+
+# Leaf nodes are terminal configuration nodes that can't have children,
+# but can have values.
+
+leafNode = element leafNode
+{
+    nodeNameAttr,
+    command,
+    properties
+}
+
+# Normal and tag nodes may have children
+children = element children
+{
+    (node | tagNode | leafNode)+
+}
+
+# Nodes may have properties
+# For simplicity, any property is allowed in any node,
+# but whether they are used or not is implementation-defined
+
+
+properties = element properties
+{
+    help? &
+    completionHelp*
+}
+
+# All nodes must have "name" attribute
+nodeNameAttr = attribute name
+{
+    text
+}
+
+# Ordinary nodes and tag nodes can have "owner" attribute.
+# Owner is the component that is notified when node changes.
+ownerAttr = attribute owner
+{
+    text
+}
+
+
+
+# help tags contains brief description of the purpose of the node
+help = element help
+{
+    text
+}
+
+command = element command
+{
+    text
+}
+
+# completionHelp tags contain information about allowed values of a node that is used for generating
+# tab completion in the CLI frontend and drop-down lists in GUI frontends
+# It is only meaninful for leaf nodes
+# Allowed values can be given as a fixed list of values (e.g. <list>foo bar baz</list>),
+# as a configuration path (e.g. <path>interfaces ethernet</path>),
+# or as a path to a script file that generates the list (e.g. <script>/usr/lib/foo/list-things</script>
+completionHelp = element completionHelp
+{
+    (element list { text })* &
+    (element path { text })* &
+    (element script { text })*
+}
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