Policy document is clear and well-founded at heart (9)
I believe the answer is:
manifesto
'policy document' is the definition.
'clear and well-founded at heart' is the wordplay.
'clear' becomes 'manifest' (synonyms).
'and' means one lot of letters go next to another.
'well founded at heart' becomes 'o' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'manifest'+'o'='MANIFESTO'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for manifesto that I've seen before include "Public declaration of intent" , "electoral programme" , "Written declaration of opinions" , "statement of policy" , "Declaration of intentions by a political party" .)