<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
a	O
window	B-Library
class	I-Library
is	O
fundamental	O
to	O
the	O
Microsoft	B-Application
Windows	I-Application
(	O
Win16	B-Library
,	O
Win32	B-Library
,	O
and	O
Win64	O
)	O
operating	B-General_Concept
systems	I-General_Concept
and	O
its	O
Application	B-Application
Programming	I-Application
Interface	I-Application
(	O
API	B-Application
)	O
.	O
</s>
<s>
It	O
finally	O
tells	O
the	O
operating	B-General_Concept
system	I-General_Concept
how	O
much	O
additional	O
storage	O
space	O
is	O
needed	O
for	O
the	O
class	O
and	O
each	O
window	O
created	O
from	O
it	O
.	O
</s>
