/
(                 # Assuming you want capture these lines.
  (?:             # Group each line.
     ^            # Beginning of the line.
     .{0,40}$\n?  # 0 to 40 chars, an end-of line and optional newline. 
  ){1,4}          # 1 to 4 lines. (0 will permit an empty match.)
)                 # Done capturing.
/mx;              # /m so that ^ anchor works, /x for comments.

##</code><code>##


/
(               # Assuming you want capture these lines.
  (?:           # Group each line.
     ^          # Beginning of the line.
     .{0,40}$   # 0 to 40 characters followed by an end-of-line.
     \n?        # An optional newline. 
  ){1,4}        # 1 to 4 lines. (0 will permit an empty match.)
)               # Done capturing.
/mx;            # /m so that ^ anchor works, /x for comments.