The most common and most likely answer to this crossword clue is the 6 letter word PENNED
I've seen this crossword clue in The Guardian
P
E
N
N
E
D
More clues leading to the result PENNED
Buddy explains!
The straight part
We know that "Did lines/kept in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case did lines/kept in = penned.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PENNED mean?
PENNED verb- To enclose in a pen.
- To write (an article, a book, etc.).
- Winged; having plumes