Adding negative parent example

Author: mikefarah

pkg/yqlib/doc/operators/parent.md

@@ -80,7 +80,7 @@ will output
 ```
 
 ## Get the top (root) parent
-Use negative numbers to get the top parents
+Use negative numbers to get the top parents. You can think of this as indexing into the 'parents' array above
 
 Given a sample.yml file of:
 ```yaml
@@ -156,6 +156,25 @@ a:
     c: cat
 ```
 
+## N-th negative
+Similarly, use negative numbers to index backwards from the parents array
+
+Given a sample.yml file of:
+```yaml
+a:
+  b:
+    c: cat
+```
+then
+```bash
+yq '.a.b.c | parent(-2)' sample.yml
+```
+will output
+```yaml
+b:
+  c: cat
+```
+
 ## No parent
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/operator_parent_test.go

@@ -40,7 +40,7 @@ var parentOperatorScenarios = []expressionScenario{
 	},
 	{
 		description:    "Get the top (root) parent",
-		subdescription: "Use negative numbers to get the top parents",
+		subdescription: "Use negative numbers to get the top parents. You can think of this as indexing into the 'parents' array above",
 		document:       "a:\n  b:\n    c: cat\n",
 		expression:     `.a.b.c | parent(-1)`,
 		expected: []string{
@@ -56,15 +56,6 @@ var parentOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!map)::a:\n    b:\n        c: cat\n",
 		},
 	},
-	{
-		description: "N-th negative",
-		skipDoc:     true,
-		document:    "a:\n  b:\n    c: cat\n",
-		expression:  `.a.b.c | parent(-2)`,
-		expected: []string{
-			"D0, P[a], (!!map)::b:\n    c: cat\n",
-		},
-	},
 	{
 		description: "boundary negative",
 		skipDoc:     true,
@@ -116,6 +107,15 @@ var parentOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!map)::a:\n    b:\n        c: cat\n",
 		},
 	},
+	{
+		description:    "N-th negative",
+		subdescription: "Similarly, use negative numbers to index backwards from the parents array",
+		document:       "a:\n  b:\n    c: cat\n",
+		expression:     `.a.b.c | parent(-2)`,
+		expected: []string{
+			"D0, P[a], (!!map)::b:\n    c: cat\n",
+		},
+	},
 	{
 		description: "No parent",
 		document:    `{}`,