Filled figures are implemented in the Hatch class which is created via CreateHatch instruction. Also the can be linear hatched.  Please refer to the CreateHatch examples.

<?xml version="1.0" encoding="UTF-8"?>
    <!-- Description: Instruction CREATEHATCH creates Hatch using selecte entities as countours. Please select entity by mouse or by xml Instruction SELECT before calling this Instruction. -->
<!-- 
Syntax:
  <createhatch Hatchname="" Angle="" PatternScale="" Color=""/>
Attributes: 
Hatchname - string - name of Hatch, default is "SOLID" which creates a solid hatch. Other names: "Box", "Escher" and others can be found in Hatch dialog in user interface.
Angle - Double - rotation angle of hatch
PatternScale - Double - scale of hatch's pattern 
Color - sring CADSoftTools color structure - color as index or RGB
 -->
 
<cadsofttools version="2">
  <!-- Create simple rectangular Solid Hatch. Handle of polyline is saved as "@1" -->
  <add>
    <cstLWPolyline HandleSave="@1">
    <SubEntities>    
    <cstVertex Point="140,100,0"/> 
    <cstVertex Point="141,100,0"/> 
    <cstVertex Point="141,103,0"/> 
    <cstVertex Point="140,103,0"/> 
    </SubEntities>
    </cstLWPolyline>
  </add>
    <!-- Select polyline -->
  <Select Handle="@1"/>
    <!-- Create hatch -->
  <createhatch/>
  <UnSelect Handle="@1"/>
 
    <!-- Create polyline for Hatch,  -->
 
  <add>
    <cstLWPolyline HandleSave="@2">
    <SubEntities>    
    <cstVertex Point="141,109,0"/> 
    <cstVertex Point="142,112,0"/> 
    <cstVertex Point="143,109,0"/> 
    <cstVertex Point="147,109,0"/> 
    <cstVertex Point="144,107,0"/> 
    <cstVertex Point="145,105,0"/> 
    <cstVertex Point="142,107,0"/> 
    <cstVertex Point="141,105,0"/> 
    <cstVertex Point="141,107,0"/> 
    <cstVertex Point="138,108,0"/> 
    <cstVertex Point="141,109,0"/> 
    </SubEntities>
    </cstLWPolyline>
  </add>
    <!-- Select polyline -->
  <Select Handle="@2"/>
    <!-- Create hatch -->
  <createhatch hatchname="BOX" Angle="30" PatternScale="0.1"  Color="0;34;"/>
  <UnSelect Handle="@2"/>
 
  <!-- Create and select some countours for creating hatch. -->
  <add>
    <cstLine point="120,120,0"  point1="130,130,0" Color="0;3;" HandleSave="@3"/>
    <cstLine point="120,120,0"  point1="130,110,0" Color="0;3;" HandleSave="@4"/>
    <cstLine point="130,110,0"  point1="130,130,0" Color="0;3;" HandleSave="@5"/>
    <cstCircle point="100,100,0"  radius="10" Color="0;3;" HandleSave="@6"/>
  </add>
    <!-- Select contours -->
  <Select Handle="@3"/>
  <Select Handle="@4"/>
  <Select Handle="@5"/>
  <Select Handle="@6"/>
  <createhatch hatchname="SOLID" Color="0;3;"/>
  <UnSelect Handle="@3"/>
  <UnSelect Handle="@4"/>
  <UnSelect Handle="@5"/>
  <UnSelect Handle="@6"/>
 
  <fittosize />
</cadsofttools>