Question

Basically, I don’t understand what the real difference here is:

The Microsoft code for TabItem uses:

<ContentPresenter ContentSource="Header" ... />

So, when would one use the Content property instead of (or in addition to) ContentSource?

Answer 1

This property should only be used when
the ContentPresenter is in a template.
When a template contains a
ContentPresenter with ContentSource
set to “Abc”, the Content,
ContentTemplate, and
ContentTemplateSelector properties of
the ContentPresenter are automatically
aliased to Abc, AbcTemplate, and
AbcTemplateSelector, respectively.
Beginning with the .NET Framework
version 3.5 Service Pack 1, setting
ContentSource to “Abc” also causes the
ContentStringFormat property to be
aliased to AbcStringFormat.

The two most useful values for this
property are “Content” and “Header”.

(MSDN)

ContentSource apparently sets more properties at once for convenience.

---

Practically, The declaration:

<ContentPresenter ContentSource="Header" />

Performs the following initialization.

<ContentPresenter Content="{TemplateBinding Header}"
                  ContentTemplate="{TemplateBinding HeaderTemplate}"
                  ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}"
                  ContentStringFormat="{TemplateBinding HeaderStringFormat}" />

It does this for each property separately only if the dependency property exists on the templated control.