diff --git a/vlib/builtin/builtin.v b/vlib/builtin/builtin.v
index f9c39f490f..bdeac267a6 100644
--- a/vlib/builtin/builtin.v
+++ b/vlib/builtin/builtin.v
@@ -110,13 +110,24 @@ pub:
 // FieldData holds information about a field. Fields reside on structs.
 pub struct FieldData {
 pub:
-	name          string
-	attrs         []string
-	is_pub        bool
-	is_mut        bool
-	is_shared     bool
-	typ           int
-	unaliased_typ int
+	name          string // the name of the field f
+	typ           int    // the internal TypeID of the field f,
+	unaliased_typ int    // if f's type was an alias of int, this will be TypeID(int)
+	//
+	attrs  []string // the attributes of the field f
+	is_pub bool     // f is in a `pub:` section
+	is_mut bool     // f is in a `mut:` section
+	//
+	is_shared   bool // `f shared Abc`
+	is_atomic   bool // `f atomic int` , TODO
+	is_optional bool // `f ?string` , TODO
+	//
+	is_array  bool // `f []string` , TODO
+	is_map    bool // `f map[string]int` , TODO
+	is_chan   bool // `f chan int` , TODO
+	is_struct bool // `f Abc` where Abc is a struct , TODO
+	//
+	indirections u8 // 0 for `f int`, 1 for `f &int`, 2 for `f &&int` , TODO
 }
 
 pub enum AttributeKind {