On the Diceware page is this little gem:
For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at random adds about 10 bits of entropy.
By that statement, does that mean adding a random character to a random position in a Diceware word adds 10 bits to each word?
What would be the entropy per Diceware word if random printable ASCII character is used instead?
What would be the entropy per Diceware word if a random Diceware word is used as the random charactersymbol in a random position per Diceware word?
How exactly can this be calculated?