Advanced List Manipulation in Python: Merging Two Lists with Customized Logic

Question

I have two lists in Python, and I need to merge them based on specific criteria while handling duplicates intelligently. The merging logic should involve advanced operations, such as sorting, filtering, and aggregating data points from both lists.

Here are the example lists:

[code] list1 = [
    {'id': 1, 'value': 10},
    {'id': 2, 'value': 20},
    {'id': 3, 'value': 30},
]

list2 = [
    {'id': 2, 'value': 25},
    {'id': 3, 'value': 35},
    {'id': 4, 'value': 40},
]

[/code]

I want to merge these lists into a single list, applying the following rules:

1. Retain unique elements from both lists based on the 'id' field.
2. If an 'id' exists in both lists, update the 'value' field by taking the maximum 'value' from both lists.
3. Sort the merged list based on the 'value' field in descending order.

The expected merged list should look like this:

[code]merged_list = [
    {'id': 4, 'value': 40},
    {'id': 3, 'value': 35},
    {'id': 2, 'value': 25},
    {'id': 1, 'value': 10},
]
[/code]

Could someone provide a Python code sample that performs this complex list merging with the necessary criteria? I looked up merge lists in Python on a number of different sources, but despite my best efforts, I was unable to find the solution.  Include a summary of any key concepts or techniques used in the solution. I appreciate your knowledge.