Model:
        ...
        hierarchBody = HierarchBody
        ...
;

HierarchBody:
{HierarchBody}
name = 'HIERARCHY' 
element += HierarchyElement*
'END_HIERARCHY'
;

HierarchyElement:
Group | TemplateDefinition
;

Group:
'GROUP' name=ID 
elements += (GroupElement)+
'END_GROUP'
;

GroupElement:
Entity|TemplateReference|TemplateDefinition
;

Entity:
'ENTITY' name=ID 
value = Value
'END_ENTITY'
;

TemplateDefinition:
'define' 'template' name = ID '[' templatevariable=TemplateVariable ']'
elements += (Entity|TemplateReference)+
'end_define'
;

TemplateVariable:
name=ID
;

TemplateReference:
{TemplateReference}
name=ID 'references to' reference=[TemplateDefinition|ID] '[' elements=IntElementList ']'
;

HIERARCHY
 define template TemplateOfEntities[Index]
  ENTITY TemplateEntity1
    value 47
  END_ENTITY
  ENTITY TemplateEntity2
    value 11
  END_ENTITY
 end_define

 GROUP Group1
  TemplateInjection1 references to TemplateOfEntities[1..5]

  TemplateInjection2 references to TemplateOfEntities[10..15]

  if(TemplateInjection1.TemplateEntity1.value == 47)
    ENTITY Entity1G1
     value 123
    END_ENTITY
  end_if
 END_GROUP

END_HIERARCHY

grammar org.xtext.example.forum.FORUM with org.eclipse.xtext.common.Terminals

generate fORUM 

Model:
        hierarchBody = HierarchBody
;

HierarchBody:
{HierarchBody}
name = 'HIERARCHY' 
element += HierarchyElement*
'END_HIERARCHY'
;

HierarchyElement:
Group | TemplateDefinition
;

Group:
'GROUP' name=ID
elements += (GroupElement)+
'END_GROUP'
;

GroupElement:
Entity|TemplateReference|TemplateDefinition|ConditionalStatement
;

Entity:
'ENTITY' name=ID 
value = Value
'END_ENTITY'
;

TemplateDefinition:
'define' 'template' name = ID '[' templatevariable=TemplateVariable ']'
elements += (Entity|TemplateReference)+
'end_define'
;

TemplateVariable:
name=ID
;

TemplateReference:
{TemplateReference}
'reference' name=ID 'to' reference=[TemplateDefinition|ID] '[' elements=IntElementList ']'
;

Value:
	'value' value=INT
;

IntElementList:
	firstelement = INT
	(','elements+=INT)*
;

ConditionalStatement:
	'if' '(' expression=Expression ')'
	'{'
	then+=Entity+
	'}'
;

Expression:
	reference = [ReferencableElements|QUALIFIEDNAME]
;

ReferencableElements:
	Entity | TemplateReference
;

terminal ID:
	('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'_'|'0'..'9')*
;

terminal QUALIFIEDNAME:
	ID ('.'ID)*
;

HIERARCHY 

GROUP group
	define template Template[Index]
		ENTITY tempentity
			value 1
		END_ENTITY
	end_define
	
	reference Reference1 to Template[1,3]
 
  if (group.Reference1)
  {
	ENTITY entity
		value 1
	END_ENTITY
  }
END_GROUP

END_HIERARCHY

terminal QUALIFIEDNAME:	ID ('.'ID)*; 

Reference returns Expression:
	{Reference}
	reference = [ConfkeyOrOption|QUALIFIEDNAME] 
;