What does the <service> tags in atlassian-plugin-context do?

[Tilwin Joy]

There are <service> tags such as the following in atlassian-plugin-context file in atlassian-rest plugin.

<service interface="com.sun.jersey.spi.container.ResourceFilterFactory">
    <service-properties>
        <beans:entry key="plugin" value="com.atlassian.plugins.rest"/>
    </service-properties>
    <beans:bean class="com.atlassian.plugins.rest.common.feature.jersey.DarkFeatureResourceFilterFactory" autowire="constructor"/>
</service>

I'd like to understand what they do, especially when does these factory methods execute in the plugins life cycle.