what can be put into node tag args=" HERE"

edit

It seems like the args attribute in <node> tag can have many values and I am wondering what kinds of values we should assign to args attributes in <node> tag. For example, the following launch file:

<launch>

    <arg name="base" default="$(env BULLETSIM_SOURCE_DIR)/data/bagfiles"/>
    <arg name="filename" />
    <arg name="camera" default="kinect1"/>

    <include file="$(find openni_launch)/launch/openni.launch">
        <arg name="camera" value="$(arg camera)" />
        <arg name="load_driver" value="false" />
        <arg name="depth_registration" value="true" />
    </include>

    <node name="rosbag_$(arg camera)" pkg="rosbag" type="play" args="-k --clock $(arg base)/$(arg filename).bag" /> 

    <!--
    <node pkg="rosbag" type="play" name="rosbag" args="-l $(arg base)/$(arg filename).bag /kinect1:=/kinect1_rec" /> 
    <node pkg="image_transport" type="republish" name="image_transport_color" args="theora in:=/kinect1_rec/rgb/image_rect_color raw out:=/kinect1/rgb/image_rect_color" />
    -->

</launch>

Another launch file is like this:

<launch>

    <arg name="camera" default="kinect1"/>
    <arg name="online" default="true"/>
    <arg name="bus" default="1"/>
    <arg name="filename"/>

    <group if="$(arg online)">
        <param name="use_sim_time" value="false" />
        <include file="$(find openni_launch)/launch/openni.launch">
            <arg name="camera" value="$(arg camera)" />
            <arg name="device_id" value="$(arg bus)@0" />
            <arg name="depth_registration" value="true" />
        </include>
    </group>
    <group unless="$(arg online)">
        <param name="use_sim_time" value="true" />
        <include file="play_cloud.launch">
            <arg name="camera" value="$(arg camera)" />
            <arg name="filename" value="$(arg filename)" />
        </include>
    </group>

    <node name="drop1" pkg="topic_tools" type="drop" args="/$(arg camera)/depth_registered/points 2 3 /drop/points"/>
    <node name="preprocessor" pkg="binary_symlinks" type="qpreprocessor_node" output="screen"  args="--inputTopic=/drop/points --downsample=0.008 --removeOutliers=true --outlierRadius=0.016 --outlierMinK=0 --clusterMinSize=15 --zClipLow=-0.02 --backgroundRead=false --backgroundFile=/home/alex/Desktop/preprocessor.yml" /> 

</launch>