Ruby has interesting behavior with strings. "A""B" return AB How it works?

Question

How works strings in Ruby?

 irb
2.7.2 :001 > "A""B"
 => "AB" 
2.7.2 :002 > a = "A""B"
 => "AB" 
2.7.2 :003 > a
 => "AB" 
2.7.2 :004 > x = "X"'Y'"Z"
 => "XYZ" 
2.7.2 :005 > x
 => "XYZ"

Please tell me why it works like this