When it comes to web development, mastering PHP functions is crucial for building dynamic and interactive websites. Here are the 10 essential PHP functions that every developer should be familiar with:

1. strlen(): This function returns the length of a string, allowing developers to validate user input.
2. strpos(): It searches for a substring within a string, which is handy for data parsing.
3. array_push(): Use this function to add one or more elements to the end of an array.
4. json_encode(): Converting arrays or objects into a JSON string, this function is vital for API interactions.

Continuing with our list of essential PHP functions, here are more that can help streamline your coding process:

6. date(): Use this function to format date and time, which is essential for displaying timestamps accurately.
7. foreach(): This is a powerful looping structure that allows you to iterate over arrays effortlessly.
8. require_once(): It includes and evaluates a specified file, making it easier to manage dependencies.
9. mysqli_connect(): This function establishes a connection to a MySQL database, a fundamental operation for any web application.
10. header(): Necessary for sending raw HTTP headers, this function is key for controlling content types and redirects.

Understanding Object-Oriented Programming (OOP) is essential for PHP developers looking to create efficient and reusable code. In PHP, OOP allows programmers to model real-world entities using classes and objects. A class serves as a blueprint for creating objects, encapsulating both data and behaviors, while objects are instances of these classes. By employing concepts like inheritance, encapsulation, and polymorphism, developers can build scalable applications that are easy to maintain and extend.

To get started with OOP in PHP, it's crucial to understand its core principles. First, encapsulation involves bundling the data (properties) and methods (functions) that operate on the data into a single unit known as a class. Second, inheritance allows a new class to inherit properties and methods from an existing class, promoting code reusability. Lastly, polymorphism enables methods to be used in different ways based on the object that is invoking them. By mastering these principles, developers can enhance the functionality and adaptability of their PHP applications.

As we delve into PHP in 2023, it's essential to recognize its enduring significance in the web development landscape. Despite the emergence of newer programming languages and frameworks, PHP continues to power a substantial portion of the web, including major platforms like WordPress and Facebook. This resilience is attributed to its ease of use, extensive documentation, and a vast ecosystem of libraries and frameworks. Furthermore, with the release of PHP 8, developers have witnessed significant performance improvements and modern features that make coding in PHP more efficient and enjoyable than ever.

Moreover, the community surrounding PHP remains robust, providing a wealth of resources for both novice and seasoned developers. New tools and frameworks, such as Laravel and Symfony, have rejuvenated the language, enabling developers to build complex applications effortlessly. Additionally, as the demand for PHP remains strong in the marketplace, learning this language can open numerous career opportunities for developers. In conclusion, PHP is not only relevant in 2023 but is also evolving, proving its place in modern development.