Key is an Expression Type which extracts a value from a key value collection.
Expression Types are used in Search Fields.
The Expression Types to choose between when configuring a Search Field is:
How to Add or manage Search Field.
This default extractor finds the provided key in the message context and grabs the value.
A Key value can be tested for using the Test Expression tab. Simply add the relevant Message Context (any number of values can be added), and enter your Expression. If you get it right, the proper value should be extracted by the Logging Service in the background and presented in the browser.
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