Any method of enlarging the sail area in light winds, and reducing it  again in high winds, without having to change sails altogether (as is still done sometimes in the Mediterranean and the Arab area to this day) was a highly desirable feature, as can be imagined. Two fundamentally different systems were used to this end: the reef for reducing the sail area, and the bonnet for increasing it. The reef is the older method, being invented in the 12th century by the descendants of the Scandinavian Vikings, the Normans. The bonnet came from the Mediterranean area (whether from Italy, Spain or Portugal is not clear), and by the beginning of the 15th century it had displaced the reef. The latter was reintroduced in the middle of the 17th century and had, in its turn, virtually superseded the bonnet by the end of the 17th century .

   The bonnet 
The bonnet was a strip of canvas - often two strips until the end of the 16th century on large ships - which was attached to the parent sail by a series of rope loops. The bonnet loops were pulled through eyelets at the foot of the parent sail, pulled across to the adjacent eyelet, and the next loop pulled through it. This produced a linked chain system, the last loop of which was made fast at the clew of the parent sail. If this seizing was loosened, all the loops were released, and the bonnet could be taken down.
    For modelling purposes, it is advisable to "sew" the loops, as shown in the drawing, rather than to try to attach the loops to the bonnet first. and then pull them through, as per full-size practice. Please note that the chain of loops was always situated on the fore side of the sail. To make it easier for the sailors to match the eyelet with the right loop when putting up the bonnet, it was a widespread practice on ships of Catholic nations (Spain, Portugal, Italy, and to some extent France) to write the first few words of the "Ave Maria" on the foot of the parent sail and the head of the bonnet, so that the sailors could align the same letters at top and bottom.
   
   The reef
The reef points were short tapered lengths of flat plaited cordage which reeved though the sail and hung freely in front of and behind the sail, being knotted on both sides to prevent them pulling through. To avoid the sail tearing these points were reinforced with reef bands sewn onto both sides of the sail.
  On sails of the 13th to the 15th centuries the reef points were located in the lower part of the sail, but after their reintroduction in the 17th century they were fitted in the upper part - otherwise they were identical. Around 1655 a single row of reef point was introduced on the topsails, and around 1680 this was doubled; in the 18th and early 19th century up to four rows were used. When the topsail was divided into the lower topsail and the upper topsail in the middle of the 19th century , the reef points remained on the upper topsail, but were reduced to one or -at most -two rows.
    A single row of reef points was used on the lower sails too from 1680 on, although it was common practice just to sew eyelets in the reef band until the middle of the 18th century , the reef points only being fitted when required. No reef points were carried on the topgallant sails; at best a reef band with eyelets.
All gaff sails also carried reef points, also the spritsail, often the fore topmast staysail, and occasionally the inner jib.