diff --git a/node.go b/node.go
index 638f974..a8c4c39 100644
--- a/node.go
+++ b/node.go
@@ -42,6 +42,16 @@ func (pe parseErr) Unwrap() error {
 
 //
 
+type ParseContext int
+
+const (
+	TopLevelContext         ParseContext = iota // We are free to inject entire additional statements
+	RvalueFreeContext                           // We are free to make `x, ok := foo(); ok` transformations e.g. for array_key_exists()/isset()
+	RvalueRestrictedContext                     // We are not free to make semicolon transformations
+)
+
+//
+
 type conversionState struct {
 	currentClassName       string
 	currentClassParentName string