The module also requires the libxml library (http://www.xmlsoft.org/); however, this is included by default in PHP 5, at least under Windows.
Under Unix/Linux/Mac, libxml has to be installed, at least in version 2.5.4 (however, at the time of writing, version 2.6.11 is current and is included in the Windows binaries of PHP 5.0.1). Also, PHP must be configured using the configuration switch --enable-soap.
As usual, calling phpinfo() shows whether the installation succeeded. Figure 18.2 shows the successa soap enTRy is in the module list.
Figure 18.2. Success: The SOAP module has been loaded.
The SOAP module can cache WSDL descriptions, which makes the repetitive use of the SOAP functions much more performant. The php.ini options in Table 18.1 fine-tune this behavior: