I keep hearing about matching holiday pajamas. Is this really a thing?

I don't mean a thing like the Elf on the Shelf, which I can easily ignore, at least so far. The day may come, I suppose, when guests feel free to look around hosts' houses and say, "Oh no. Please don't tell me you're one of those people who doesn't have an elf."

They already hold people to other holiday traditions. They enter the kitchen on Thanksgiving, sniff the air like a Pinkerton detective and say, "Wait, you aren't having turkey? On Thanksgiving?" You'd think baking a ham on the third Thursday in November was like sacrificing your firstborn on the winter solstice.

Holiday customs are so embedded in our national consciousness that flouting them puts a person in danger of social ostracism. Remember Philip Nolan, the man without a country? He probably thought it would be OK this one time to serve sweet potatoes without miniature marshmallows on top. I made roast beef and Yorkshire pudding on a Christmas or two -- not recently; this was when I was young and brash -- but I always roasted a turkey breast, too, as protection against charges of sedition.

Anyway. "Matching holiday pajamas for the whole family, including dogs and cats," the advertisements say. Accompanying the text is a picture of a family group all in red plaid, looking either cute as a button (in the cases of small children and the dog), or sheepish and awkward (in the cases of everyone else except the cat). The cat looks distant, probably because in his head he's already turned himself in to the humane society, trusting that any other adoptive family has to be better than this one.

While researching the pajama phenomenon online, I found a Target ad featuring its own associates. No fewer than 21 families posed in matching flannel -- plaids, Santas, Grinches, elves, reindeer, penguins, menorahs and, inexplicably, Star Wars. Two of the families had dogs. You know how when someone says, "There's a bee on your head!" you freeze, saying, "Get it off me! Get it off me!"? These dogs were waiting for someone to get it off them.

Now, I wouldn't dream of critiquing the various patterns. If penguins rampant would be your family crest if you had one, fine.

Furthermore, my own favorite sleeping garment is a gray T-shirt so old and worn as to be literally translucent. Age has caused the seams to separate from the shirt to the point that I often put my head through a random loop instead of the standard neck opening and have to back out and start over. This both amuses my husband a little too much and disqualifies me from having an opinion.

Not that I came here to judge. I came here with questions. Why are matching pajamas a thing?

Is it for Christmas photo cards -- or in the case of those menorahs, Hanukkah photo cards? Sending a matching PJs picture along with your Christmas letter gives people visual context: They'll see baby Tim at the top of his Tiny Tots swim class; little Jane as Lady Bracknell in the third-grade production of "The Importance of Being Earnest;" Mom the high-powered attorney arguing a point of corporate law; Dad the dermatologist performing Mohs surgery; and Mittens the cat looking murderous, everyone in their red and green elf pajamas and pointy caps. These are images that will linger all year.

Perhaps the pajamas are for Christmas Eve, when the family gathers for carols in the little village church. Or for when everyone goes a-wassailing.

If the pajamas are meant to be worn every night all winter, a warning: Although you might talk the two-legged family members, even the self-conscious, eye-rolling 13-year-old, into it, a cat will wear pajamas once. He will not wear them twice.

Your only hope for that pair is that another family member will have a good-natured baby by this time next year.

Write to Margo Bartlett at margo.bartlett@gmail.com.