Snippet

Snippet[doc] gives a snippet of text from a document or other content object.

Snippet[doc,n] gives about n lines from the beginning. 

Snippet[doc,-n] gives about n lines from the end.

Snippet[doc,n1;;n2] gives a span from lines n1 to n2

Snippet[doc,n1;;n2;;n3] gives a span from lines n1 to n2 in steps of n3.

Snippet[ContentObject[…],SearchResultObject[…]] gives contextual snippets from a content object based on search results.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.