String#split takes an argument to limit the number of returned matches. Once the limit is reached, the rest of the string is returned as one match even if it contains more delimiters.

For example, say we are parsing a string whose first two lines are always headers and the rest is the body:

text = <<-TEXT
header1 = value
header2 = value
the body
keeps going
on over
multiple lines
TEXT

A simple split on newlines would create an array with each line as an individual element:

text.split("\n")
# => ["header1 = value",
#     "header2 = value",
#     "the body",
#     "keeps going",
#     "on over",
#     "multiple lines"]

Since we know there are two headers and a body, we can tell split to stop splitting once we have three segments:

text.split("\n", 3)
# => ["header1 = value",
#     "header2 = value",
#     "the body\nkeeps going\non over\nmultiple lines"]