This is a reference to be used for Model rule validation and is compiled from the Yii documentation and code. The purpose is to have all the information gathered in one place instead of scattered. This reference is not an intro.
See The Definitive Guide to Yii, Declaring Validation Rules for a tutorial.
Relational databases do not support inheritance so if we need to represent it, we have to somehow store meta info while keeping performance by minimizing JOINs. One way to solve this problem is using single table inheritance. All fields for the whole class tree are stored in a single table. Class name is stored in the type field of the same table.
The yii2-field-range extension enables you to easily setup ActiveField range fields with Bootstrap styling. You basically can setup two attributes joined together like a single field with combined validation error block.
You may have scenarios, where you want to store a specific array configuration to the database. A classic example could be saving Yii widget configuration to the database and then retrieving it at runtime, with dynamic parameters set. This wiki discusses one of the approaches to do this. Let's consider you have something like the NavBar configuration below to store in the db: