Changing Visual State in Custom Control

Call VisualStateManager.GoToState(control, strStateName, useTransitions)
strStateName is mapped to a TemplateVisualStateAttribute of the control class.

PrintDocument

sample: http://web.archive.org/web/20101128170826/http://silverlightips.net/2010/03/27/multi-page-printing-in-silverlight/
including:
PrintDocument .PrintPage (event) .Print (method)
PrintPageEventArgs .PageVisual (UIElement) .PrintableArea (Size) .HasMorePages

Also usage of Canvas.TopProperty in SetValue

GetTemplateChild vs. FindName

http://msdn.microsoft.com/en-us/library/system.windows.controls.control.gettemplatechild(v=vs.95).aspx

http://social.msdn.microsoft.com/forums/en-US/wpf/thread/eb509920-e2c3-43d7-987b-6f67cbd544c9

OnApplyTemplate, Loaded, and LayoutUpdated

For pros and cons: http://msdn.microsoft.com/en-us/library/system.windows.frameworkelement.loaded(v=vs.95).aspx
http://msdn.microsoft.com/en-us/library/system.windows.frameworkelement.onapplytemplate(v=vs.95).aspx

TemplateBindings

TemplateBindings are special bindings usable only in ControlTemplates (no DataTemplates), whose binding source is the control instance on which the template is applied.

http://forums.silverlight.net/t/158826.aspx/1

Dependency Properties vs. Attached Properties

Attached Properties use an accessor style that XAML parser can use, i.e. SetPropertyName
As opposed to regular dependency properties that use regular Set/Get accessors.

For attached properties see: http://msdn.microsoft.com/en-us/library/cc265152(v=vs.95).aspx

For regular dependency property requirements see Checklist for Defining a Dependency Property
Nice sample of custom dependency object here (bottom)

Silverlight 4 Validation

This two-part series sums it up:
http://www.silverlightshow.net/items/The-validation-story-in-Silverlight-Part-1.aspx
http://www.silverlightshow.net/items/The-validation-story-in-Silverlight-Part-2.aspx

SL 3 supports ValidatesOnExceptions=True, NotifyOnValidationError=True
Throw exceptions in setters. Optionally use validation attributes on model properties: this requires Validator.ValidateProperty(value, new ValidationContext... in setter
Can use CustomValidation attribute and sdk:ValidationSummary tag

SL4 introduces IDataErrorInfo plus ValidatesOnDataErrors=True tag
and INotifyDataErrorInfo plus ValidatesOnNotifyDataErrors=True

Can customize the validation states in Blend: Default transition, Valid, InvalidUnfocused, InvalidFocused