More examples with screenshots are planned. Sorry for only giving one example.
Here we go:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<configuration>
<source>
<entity id="e1" name="string" label="String field" type="string" readonly="true"/>
<entity id="e2" name="integer" label="Integer field" type="integer" required="true">
<rule expr="$integer ge 16" msg="Integer must be greater than 15" mode="post"/>
</entity>
<entity id="e3" name="float" label="Float field" type="float">
<rule expr="$float lt 100" msg="Float must be lower than 100" mode="post"/>
<help>This is is a very long helptext which should span over
multiple rows. Further the will check if there are further html
tags allowed.</help>
</entity>
<entity id="e4" name="date" label="Date field" type="date" autocomplete="off" number="1">
<renderer type="datepicker"/>
<help>This is my helptext</help>
</entity>
<entity id="e5" name="select" label="Select field" type="string">
<help>This is my helptext</help>
<renderer type="dropdown"/>
<options>
<option value="1">Option 1</option>
<option value="2">Option 2</option>
<option value="3">Option 3</option>
<option value="4">Option 4</option>
</options>
</entity>
<entity id="e6" name="optional" label="Optional field">
<help>This field is only shown if the Dropdown has selected option 4</help>
</entity>
</source>
<form id="example1" css="testcss" autocomplete="off" method="POST" action="" enctype="multipart/form-data">
<snippet ref="s1"/>
</form>
<snippet id="s1">
<row>
<col><field ref="e3"/></col>
<col><field ref="e4"/></col>
</row>
<row>
<col><field ref="e5"/></col>
</row>
<snippet ref="s2"/>
</snippet>
<snippet id="s2">
<row>
<col><field ref="e1"/></col>
<col><field ref="e2"/></col>
</row>
<row>
<if type="readonly" expr="$select == 4">
<col><field ref="e6"/></col>
</if>
</row>
</snippet>
</configuration>