Instruction: Parse the product information to locate the target attribute, and then provide the extracted value of the target attribute and its source in the output, specifying None if the attribute is not present.

Input:
Product title: White A7 Self Seal Envelopes - 50 Envelopes - Fits 5" x 7" Invitations / Greeting Cards - Great for Weddings
Product description: Desktop Publishing Supplies™ Brand Peel & Seal White A7 Self Seal Envelopes provide an easier, cleaner, and more sanitary way to send invitations, greeting cards, or letters! No water needed, simply remove the strip and press to seal your envelopes securely. These White A7 Envelopes are made from a 24lb bond / 60lb text (90 gsm) white paper stock and are inkjet and laser printer compatible. These white A7 self seal envelopes measure 5 1/4" x 7 1/4" each and feature a square flap. 50 Envelopes
Product feature: A7 Size Envelope (5 1/4" x 7 1/4"), 24lb bond / 60lb text (90 gsm) White Paper Stock, Inkjet & Laser Compatible, Square Flap - With Easy Peel & Seal Strip, 50 Envelopes
Product brand: Desktop Publishing Supplies, Inc.
Target attributes: Size
Answer: attribute: size
value: a7
source: product title
attribute: size
value: a7
source: product description
attribute: size
value: a7
source: product feature