PREFIX : <http://example.org/>
SELECT *
WHERE
  (?x ?y ?z) (?a ?b ?c)

  # Optional, [] syntax
  [ (?x ?y ?z) ]
  [ (?x ?y ?z) AND ?z < 2 ]
  
  [ (?x ?y ?z) AND ( ?z < 2 ) ]
    
  [ (?x ?y ?z) (?x ?y ?z) ]
  [ (?x ?y ?z) (?x ?y ?z) AND ?z < 2 ]
  [ (?x ?y ?z) [ (?x ?y ?z) ] ]
 
  # OPTIONAL keyword
  OPTIONAL (?x ?y ?z) 
  OPTIONAL { (?x ?y ?z) (?x ?y ?z) AND ?z < 2 }

  # GRAPH
  GRAPH ?src (?x ?y ?z)
  GRAPH ?src { (?x ?y ?z) (?a ?b ?c) }

  # Careful - AND does not bind to the GRAPH pattern
  GRAPH ?src (?x ?y ?z) AND ( ?z < 2 )

  # It parses like (adding explicit grouping for clarity:)
  { { GRAPH ?src (?x ?y ?z) } AND ?z < 2 }

  # Not as:
  GRAPH ?src { (?x ?y ?z) AND ?z < 2 }

  # GRAPH/OPTIONAL mix 
  GRAPH ?src [ (?x ?y ?z) ]
  [ GRAPH ?src (?x ?y ?z) ]

  OPTIONAL { (?x ?y ?z) GRAPH ?src ( :x :y :z ) }
  OPTIONAL { (?x ?y ?z) OPTIONAL { ( :x :y :z ) } }
  OPTIONAL GRAPH ?src ( ?x ?y ?z )