If you want to customize a dialog window, check the source code of a plugin that creates it (e.g. _source/pluginName/dialogs/pluginDialog.js).
The contents entry defines a dialog window tab. Each UI element (text field, checkbox, button, etc.) is defined using the elements array.
Below is an example of a dialog window tab entitled First Tab that contains a text field and a checkbox.
contents :
[
{
id : 'tab1',
label : 'First Tab',
title : 'First Tab Title',
accessKey : 'Q',
elements :
[
{
type : 'text',
id : 'sampleText1',
label : 'Sample Text 1',
'default' : 'Hello world!'
},
{
type : 'checkbox',
id : 'sampleCheckbox',
label : 'This checkbox is selected by default',
'default' : true
}
]
}
]