Why can't I define key bindings for certain key combinations

[reduckted]

I was writing an extension and wanted to add a key binding to Ctrl+Shift+T. So I added this to the .vsct file:

<KeyBinding editor="guidVSStd97" guid="MyPackage" id="MyCommand" mod1="Control Shift" key1="T"/>

I start Visual Studio, press Ctrl+Shift+T and... nothing happens. I checked the keyboard shortcuts in Tools - Options and my command didn't have any shortcut keys against it. 😕

I was sure I'd defined the key binding correctly, so I tried a different key - R. I start Visual Studio again, press Ctrl+Shift+R and this time my command runs.

Well now I'm confused, so I add a key binding for every letter of the alphabet:

<KeyBindings>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="A"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="B"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="C"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="D"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="E"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="F"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="G"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="H"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="I"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="J"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="K"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="L"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="M"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="N"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="O"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="P"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="Q"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="R"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="S"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="T"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="U"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="V"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="W"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="X"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="Y"/>
  <KeyBinding editor="guidVSStd97" guid="KeyBindingTest" id="TestCommand" mod1="Control Shift" key1="Z"/>
</KeyBindings>

I start Visual Studio and take a look at the shortcut keys assigned to my command and this is what I see:

What's strange is that I can manually add a key binding for Ctrl+Shift+T (and all of the other missing key bindings) via Tools - Options. Is there a reason why certain key combinations cannot be defined in the .vsct file?

[madskristensen]

You can't assign keybindings to your command that are already used for other commands in the same scope. You can assign it in a narrower scope, for instance for your language service. A narrower scope wins over the Global scope.

Some keybindings are special and can't be used for anything. That includes Ctrl+K and Ctrl+T which is locked to be a two-key sequenced keybinding