V2 low-base docs in place

refactored constants a little also to clean things up.

datamodel/low/base/xml.go

@@ -1,21 +1,30 @@
 package base
 
 import (
-    "github.com/pb33f/libopenapi/datamodel/low"
-    "github.com/pb33f/libopenapi/index"
-    "gopkg.in/yaml.v3"
+	"github.com/pb33f/libopenapi/datamodel/low"
+	"github.com/pb33f/libopenapi/index"
+	"gopkg.in/yaml.v3"
 )
 
+// XML represents a low-level representation of an XML object defined by all versions of OpenAPI.
+//
+// A metadata object that allows for more fine-tuned XML model definitions.
+//
+// When using arrays, XML element names are not inferred (for singular/plural forms) and the name property SHOULD be
+// used to add that information. See examples for expected behavior.
+//  v2 - https://swagger.io/specification/v2/#xmlObject
+//  v3 - https://swagger.io/specification/#xml-object
 type XML struct {
-    Name       low.NodeReference[string]
-    Namespace  low.NodeReference[string]
-    Prefix     low.NodeReference[string]
-    Attribute  low.NodeReference[bool]
-    Wrapped    low.NodeReference[bool]
-    Extensions map[low.KeyReference[string]]low.ValueReference[any]
+	Name       low.NodeReference[string]
+	Namespace  low.NodeReference[string]
+	Prefix     low.NodeReference[string]
+	Attribute  low.NodeReference[bool]
+	Wrapped    low.NodeReference[bool]
+	Extensions map[low.KeyReference[string]]low.ValueReference[any]
 }
 
+// Build will extract extensions from the XML instance.
 func (x *XML) Build(root *yaml.Node, _ *index.SpecIndex) error {
-    x.Extensions = low.ExtractExtensions(root)
-    return nil
+	x.Extensions = low.ExtractExtensions(root)
+	return nil
 }