What is the expected schema for GUI forms?

We have a lot of GUI forms in our project. A few of them are broken (for years). I decided to fix it. I know it is discouraged to manually edit those XML files, but here we are. I don't see any way around it (other than recreating those forms from scratch which is a risky and time-consuming strategy)

In case you're wondering what I mean by “broken”, it's this. The screenshot is taken after trying to open the form file associated with BookingPane

After investigation, I found out that BookingPane is actually fine, the problem is with its nested form, GraphPane. I commented in and out parts of the GraphPane form, and here's what I discovered. When you comment out the last declared component, it's rendered fine in the IDE. The snippet below is the file in full

BookingHeader used to contain some paintComponent() code, but now I removed all of it, and the problem still persists

```form

<?xml version="1.0" encoding="UTF-8"?>
<form xmlns="http://www.intellij.com/uidesigner/form/" version="1" bind-to-class="graph.GraphPane">
 <grid id="27dc6" binding="mainPanel" layout-manager="GridBagLayout">
   <constraints>
     <xy x="20" y="20" width="704" height="400"/>
   </constraints>
   <properties/>
   <border type="none"/>
   <children>
     <scrollpane id="3b41b" binding="bookingScrollPane">
       <constraints>
         <grid row="1" column="0" row-span="1" col-span="1" vsize-policy="7" hsize-policy="7" anchor="0" fill="3" indent="0" use-parent-layout="false">
           <minimum-size width="700" height="-1"/>
           <preferred-size width="700" height="-1"/>
         </grid>
         <gridbag weightx="1.0" weighty="1.0"/>
       </constraints>
       <properties>
         <minimumSize width="700" height="-1"/>
         <verticalScrollBarPolicy value="22"/>
       </properties>
       <border type="none"/>
       <children>
         <component id="accb1" class="booking.BookingPanel" binding="bookingPanel">
           <constraints/>
           <properties>
             <background color="-1"/>
           </properties>
         </component>
       </children>
     </scrollpane>
     <grid id="25314" layout-manager="BorderLayout" hgap="0" vgap="0">
       <constraints>
         <grid row="0" column="0" row-span="1" col-span="1" vsize-policy="3" hsize-policy="3" anchor="0" fill="3" indent="0" use-parent-layout="false"/>
         <gridbag weightx="0.0" weighty="0.0"/>
       </constraints>
       <properties/>
       <border type="none"/>
       <children> <!--
         <component id="e6331" class="booking.BookingHeader" binding="bookingHeader">
           <constraints border-constraint="Center"/>
           <properties>
             <background color="-1"/>
             <focusable value="true"/>
             <minimumSize width="10" height="17"/>
             <opaque value="true"/>
             <preferredSize width="10" height="17"/>
           </properties>
         </component> -->
         <grid id="b94e8" layout-manager="GridLayoutManager" row-count="1" column-count="1" same-size-horizontally="false" same-size-vertically="false" hgap="-1" vgap="-1">
           <margin top="0" left="0" bottom="0" right="0"/>
           <constraints border-constraint="East"/>
           <properties>
             <maximumSize width="17" height="15"/>
             <minimumSize width="17" height="15"/>
             <preferredSize width="17" height="15"/>
           </properties>
           <border type="none"/>
           <children/>
         </grid>
       </children>
     </grid>
   </children>
 </grid>
</form>

```

```java

package booking;

import javax.swing.*;
 

// removed all the code
public class BookingHeader extends JPanel {}

```

If I reintroduce the last component, I get a similar “broken” effect:

What's wrong with the form file?

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