Visualforce custom components

There are lots of standard Visualforce components (such as <apex:detail>, <apex:pageBlock>, <apex:pageBlockTable>, and <apex:relatedList>) that can be reused in Visualforce pages. A standard Visualforce component is a prebuilt, encapsulated code segment. These standard Visualforce components are built according to common usage. They are ready to be used in Visualforce pages. The Force.com platform allows us to build our own Visualforce components. Just as functions work in a programming language, custom Visualforce components allow us to encapsulate the common design patterns and reuse those patterns in one or more Visualforce pages.

The Force.com platform allows us to develop custom Visualforce components that can be reused within a particular application. Custom components can be developed using both Apex and Visualforce. For example, suppose we want to create an employee summary with his/her recent leaves and we need to use this functionality...