IBM PCjr Manual page 77

CapsLock Mode
To put the keyboard into the CapsLock mode, press the
CapsLock key once and release it.
In the CapsLock mode, the letters A through Z appear
in uppercase.
The keyboard stays in the CapsLock mode until you
press CapsLock again.
If you want to type a lowercase letter or a black
symbol, while the keyboard is in the CapsLock mode,
you have to press the Shift key.
You can type lowercase characters while in the
CapsLock mode by pressing and holding the Shift key
and then pressing the key for the character you have
chosen to appear in lowercase.
Keyboard 3-17