What is the syntax for declaring an abstract class in PHP?

 In PHP, you can declare an abstract class using the "abstract" keyword before the class declaration. An abstract class cannot be instantiated and can only be used as a parent class for other classes.

Here is the syntax for declaring an abstract class in PHP:

abstract class ClassName
{
    // properties and methods go here
}

Additionally, you can declare an abstract method in an abstract class by using the "abstract" keyword before the method declaration. Abstract methods don't have a body, and they must be implemented by any non-abstract class that extends the abstract class.

abstract class ClassName
{
    // properties and methods go here
    abstract public function abstractMethod();
}

It's worth noting that in PHP, abstract methods can only be defined in abstract classes, and classes that define an abstract method must also be defined as abstract.

Also, classes that extend an abstract class must implement all its abstract methods, otherwise, it will raise a fatal error.