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# Stack Operations
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Method chaining history management for complex query operations. The stack module maintains a history of element collections during chaining operations, allowing developers to navigate back to previous selections.
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## Capabilities
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### Chain Navigation
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Methods for navigating through the chain history during complex DOM operations.
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```javascript { .api }
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/**
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 * End the most recent filtering operation and return to the previous set of elements
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 * @returns Previous collection in the chain
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 */
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$.fn.end();
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/**
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 * Add the previous set of elements to the current collection
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 * @returns Combined collection including both current and previous elements
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 */
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$.fn.andSelf();
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```
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**Usage Examples:**
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```javascript
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// Using end() to navigate back in the chain
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$('#container')
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  .find('.item')
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  .addClass('highlighted')
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  .end()  // Back to #container
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  .addClass('processed');
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// Complex chaining with multiple end() calls
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$('.list')
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  .find('li')
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  .filter('.active')
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  .addClass('current')
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  .end()  // Back to all li elements
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  .end()  // Back to .list elements
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  .fadeIn();
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// Using andSelf() to combine sets
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$('.parent')
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  .children('.child')
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  .andSelf()  // Include both .parent and .child elements
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  .addClass('combined');
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```
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### Chain History
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The stack operations modify the following methods to support chaining history:
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- `filter()` - Maintains reference to unfiltered collection
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- `add()` - Maintains reference to original collection  
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- `not()` - Maintains reference to original collection
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- `eq()` - Maintains reference to full collection
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- `first()` - Maintains reference to full collection
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- `last()` - Maintains reference to full collection
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- `find()` - Maintains reference to search context
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- `closest()` - Maintains reference to original collection
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- `parents()` - Maintains reference to original collection
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- `parent()` - Maintains reference to original collection
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- `children()` - Maintains reference to parent collection
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- `siblings()` - Maintains reference to original collection
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### Advanced Chain Navigation
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Complex operations combining multiple chain navigation techniques.
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```javascript
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// Multi-level navigation example
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$('#form')
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  .find('input')
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  .filter('[required]')
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  .addClass('required-field')
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  .end()          // Back to all inputs
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  .filter('[type="email"]')
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  .addClass('email-field')
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  .end()          // Back to all inputs
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  .end()          // Back to #form
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  .find('button')
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  .addClass('form-button');
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// Combining andSelf() with filtering
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$('.menu')
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  .find('.menu-item')
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  .filter('.active')
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  .andSelf()      // Include both active items and their parent menu
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  .addClass('highlight-group');
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// Working with siblings and navigation
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$('.selected')
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  .siblings()
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  .addClass('sibling')
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  .end()          // Back to .selected elements
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  .addClass('original-selection');
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```
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### Chain Stack Internal Structure
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The stack maintains internal references to previous collections:
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```javascript
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// Internal structure (for reference only)
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{
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  length: 3,
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  0: element1,
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  1: element2, 
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  2: element3,
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  prevObject: previousZeptoCollection,  // Used by end()
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  context: originalContext              // Original search context
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}
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```
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This internal structure allows `end()` to return to the `prevObject` and `andSelf()` to combine the current collection with `prevObject`.