Wither following this compiler's appearance (5)
I believe the answer is:
image
'appearance' is the definition.
(I know that image is a type of appearance)
'wither following this compiler's' is the wordplay.
'wither' becomes 'age' (I am not sure about this - if you are sure you should believe this answer much more).
'following' means one lot of letters go next to another.
'this compiler's' becomes 'I'm' ('I'm', referring to the crossword compiler).
'age' put after 'im' is 'IMAGE'.
Can you help me to learn more?
(Other definitions for image that I've seen before include "Simile, metaphor" , "Mental picture; idol" , "Photo or likeness" , "Likeness U symbol" , "Simulacrum" .)