o Provide information on protocols and encodings

 can be any file wrapper

 allows for two pipelines at most – for reading & writing

o Prefix in front of a file path

file:// php://
http:// compress.zlib://
https:// compress.bzip2://
ftp:// ftps://

o Custom Wrappers

stream_wrapper_register(protocol, classname)

Registers a protocol; implementation is part of the class.

 the class implements standard functionality like reading, writing, or changing the file position
 php_user_filter is a predefined class in php and is used in conjunction with user-defined filters