# Calling .NET Instance-Level Methods

Instance-level methods (that is, non-static methods) are called by supplying an extra first argument of type `external .NET object` which is the object on which the method is to be invoked. An external .NET Object may be created by calling an extension function (e.g. a constructor) that returns an object; it may also be passed to the query or stylesheet as the value of a global parameter. Matching of method names is done as for static methods. If there are several methods in the class that match the localname, the system again tries to find the one that is the best fit, according to the types of the supplied arguments.

For example, the following XSLT stylesheet prints the operating system name and version.

    <xsl:stylesheet version="2.0"
    				xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template name="main">
      <out xmlns:env="clitype:System.Environment" xmlns:os="clitype:System.OperatingSystem">
        <xsl:variable name="os" select="env:OSVersion()"/>
          <v platform="{os:Platform($os)}" version="{os:Version($os)}"/>
      </out>
    </xsl:template>
    </xsl:stylesheet>

The equivalent in XQuery is:

    declare namespace env="clitype:System.Environment";
    declare namespace os="clitype:System.OperatingSystem";
    let $os := env:OSVersion() return
    <v platform="{os:Platform($os)}" version="{os:Version($os)}"/>

If any exceptions are thrown by the method, or if a matching method cannot be found, processing of the stylesheet will be abandoned. If the tracing option has been set (-TJ) on the command line, a full stack trace will be output. The exception will be wrapped in a `TransformerException` and passed to any user-specified `ErrorListener` object, so the `ErrorListener` can also produce extra diagnostics.

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