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Using old code with new versions of PHP

Now that PHP has grown to be a popular scripting language, there are a lot of public repositories and libraries containing code you can reuse. The PHP developers have largely tried to preserve backwards compatibility, so a script written for an older version will run (ideally) without changes in a newer version of PHP. In practice, some changes will usually be needed.

Two of the most important recent changes that affect old code are:

For more details on these changes, see the section on predefined variables and links therein.