Change record status: 
Project: 
Introduced in branch: 
11.3.x
Introduced in version: 
11.3.0
Description: 

A new constraint Serialized has been added to Drupal core. The constraint can be used to validate that a value is serialized string, and it does this validation by confirming the value can be successfully unserialized.

The first usage is in layout_builder.schema.yml, to validate the block_serialized property in the inline_block.

Impacts: 
Module developers