There are various modifiers available, which you are not required to use, for a Solidity-based function. Take a look at these:

• pure
• constant
• view
• payable

The pure functions can't read or write from the storage; they just return a value based on its content. The constant modifier function cannot write in the storage in any way. Although, the post-Solidity Version 0.4.17 constant is deprecated to make way for pure and view functions. view acts just like constant in that its function cannot change storage in any way. payable allows a function to receive ether while being called.

Multiple modifiers can be used in a function by specifying each by white-space separation; they are evaluated in the order they are written.