It is possible to ask GeoServer to render features in a style that does not exist within its own catalog. This ability to do per-request styling is also referred to as external styles.
Per-request styling of map features is part of the OGC WMS standard. Any web mapping software that conforms to the standard will contain a similar capability. As this is a book on GeoServer, we will explore GeoServer's implementation of the WMS standard.
There are three different ways in which an external style can be provided to GeoServer:
SLD=parameter can be set on the
GetMap GETrequest to point at an Internet-accessible SLD file
SLD_BODY=parameter can be set on the
GetMap GETrequest to provide the SLD document ...