## XML DOM: ownerDocument Property (Attr Object)
The `ownerDocument` property of an `Attr` (Attribute) object returns the root document element (`Document` or `XMLDocument` object) to which the attribute node belongs.
This property is highly useful when you are working with multiple documents or need to access the global document context directly from a specific attribute node.
---
## Definition and Usage
* **Purpose**: Returns the owner `Document` object of the attribute node.
* **Return Value**: A `Document` object (or `XMLDocument` object in XML contexts), which represents the root of the document containing the node.
* **Read-only**: This property is read-only.
---
## Syntax
```javascript
attrObject.ownerDocument
```
### Return Value Details
* If the attribute node belongs to a document, it returns the `Document` object.
* If the attribute node is newly created and has not yet been added to a document, this property will still return the `Document` object that was used to create it (e.g., via `document.createAttribute()`).
* If called on a `Document` node itself, it returns `null`.
---
## Code Example
The following example demonstrates how to load an XML document (`books.xml`) and retrieve the owner document of the first attribute of the first `
` element.
### Sample XML File (`books.xml`)
```xml
Everyday Italian
Giada De Laurentiis
2005
30.00
```
### JavaScript Implementation
```javascript
// Load the XML document
const xmlDoc = loadXMLDoc("books.xml");
// Select all elements
const books = xmlDoc.getElementsByTagName('book');
// Get the first attribute of the first element (category="cooking")
const firstAttr = books.item(0).attributes;
// Retrieve the owner document of this attribute
const ownerDoc = firstAttr.ownerDocument;
// Output the results
document.write("Owner Document Object: " + ownerDoc + "
");
document.write("Node Name: " + ownerDoc.nodeName + "
");
document.write("Node Type: " + ownerDoc.nodeType + "
");
```
### Expected Output
```text
Owner Document Object:
Node Name: #document
Node Type: 9
```
*Note: `nodeType` value `9` corresponds to the `Node.DOCUMENT_NODE` constant.*
---
## Key Considerations
1. **Document vs. Owner Document**:
While `ownerDocument` returns the root document node, it is different from the global `document` object in web browsers if you are working with an external XML document loaded via AJAX or an iframe.
2. **Context Preservation**:
Even if an attribute node is detached from an element (for example, using `removeAttributeNode()`), it still retains a reference to its `ownerDocument`.
3. **Browser Compatibility**:
The `ownerDocument` property is supported across all modern web browsers and complies with the W3C DOM Core standard.
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