The compose.deadkeys property allows you to modify the characters typed at the U.S. English keyboard. When this property is set to true, the following keys can be used in combination with other keys to produce special characters.
' (single quote)
' (back single quote)
" (double quote)
^ (circumflex)
For example, pressing the ' key plus the "a" key produces an á. This feature is commonly used in European locales.
Pressing a special character key twice produces its normal value.