Callback empty

This example code will return two different results depending of the existence of the content of variable some_var

<?xml version="1.0" encoding="UTF-8"?>
<SnomIPPhoneText>
	<If condition="$(empty:$(var:some_var))">
		<Text>No variable received<br/></Text>
	</If><Else>
		<Text>Variable received<br/>some_var:$(var:some_var)</Text>
	</Else>
</SnomIPPhoneText>

Result if called with http://server/thisexample.xml#var:some_var=hello_world :

Result if called only with http://server/thisexample.xml :

• Page:
  Boolean Callbacks
• Page:
  Callback arch_series
• Page:
  Callback bool_eval
• Page:
  Callback checkbox_property
• Page:
  Callback condition
• Page:
  Callback create_url
• Page:
  Callback current_input
• Page:
  Callback current_line
• Page:
  Callback date
• Page:
  Callback display_type
• Page:
  Callback empty
• Page:
  Callback enum
• Page:
  Callback fragment
• Page:
  Callback get_cmd
• Page:
  Callback lang
• Page:
  Callback lines
• Page:
  Callback list_size
• Page:
  Callback math_eval
• Page:
  Callback max_registrations
• Page:
  Callback mod_ifc
• Page:
  Callback on_off
• Page:
  Callback phone_state
• Page:
  Callback remove_cmd
• Page:
  Callback set
• Page:
  Callback setcache
• Page:
  Callback show_feature
• Page:
  Callback status_message
• Page:
  Callback time
• Page:
  Callback urlencode
• Page:
  Callback user_displayname
• Page:
  Callback var
• Page:
  Callback var_ifc
• Page:
  Callback wifiscan
• Page:
  Callback wlang
• Page:
  Callbacks
• Page:
  Callbacks edit_mode and next_edit_mode
• Page:
  Callbacks for function keys
• Page:
  Callbacks sel and lastsel