Among a small but influential group of figures at Buckingham Palace, there is a name for it: the Middleton Rules.
It is a tacit reference to what some courtiers see as a new model of royalty that has emerged since the wedding of the Duke and Duchess of Cambridge.
And it is said to govern every aspect of life at the couple's home in Norfolk, where they are determined to raise their children, Prince George and Princess Charlotte, away from prying eyes.
The phrase first surfaced not long after Prince William and the then Kate Middleton were engaged following their eight-year courtship. It was used to describe an initiative of William's to ensure his fiancee never endured the kind of treatment meted out to his mother, Princess Diana.
They were also to prevent Kate being strait-jacketed into the royal way of doing things and allow her to strike a balance between her duties as a wife and mother and the expectation that she would undertake official engagements.
At the time, the rules were presented to the Queen and Prince Charles by William as a fait accompli. On the face of it, none of them was especially provocative and some seemed eminently sensible. But a few old Palace hands worried about just how things would work out.
Unlike Ed Miliband's risible election campaign plinth gimmick, the rules have not been cut into stone but they are proving a lot more permanent.
This week, those courtiers were wondering if those same Middleton Rules had any part in the decision by the Duchess of Cambridge not to accompany William to the wedding of socialite Daisy Dickson and Old Harrovian estate agent Bear Maclean in Devon last Saturday.
Instead, her sister Pippa took her place alongside William. Friends of Kate were privately insisting she had let it be known two weeks earlier that she would not be attending.
But the rumour-mongers were busy when it was reported that the names of Kate and William were still on the seating plan for the reception in the picture postcard village of Thurlestone.
"They were meant to be sitting on the top table," a source told the Mail. "The placement had been imaginatively written on an antique-looking mirror inside the marquee and the names included William and Catherine Wales."
Her absence triggered a flood of speculation across social media, especially when it emerged that William was in no particular hurry to leave after the wedding, staying on in the village for another night and day.
Some of the remarks were plain bitchy - "Catherine of Arrogance", for example - while others queried suggestions that this was some kind of maternity leave - "maternity leave from what exactly?" one asked.
Another tartly pointed out: "You couldn't keep Kate away from these sort of events before she got an engagement ring on her finger."
By all accounts it was a lively wedding, which lasted the whole weekend and involved a mass swim by the younger guests across the River Avon estuary at nearby Bantham.
Many of Kate and William's friends were there, including multi-millionaire film-maker Arthur Landon, whose former SAS officer father Tim was known as the "White Sultan" for his derring-do in Oman, and the Sky Sports Formula 1 presenter Natalie Pinkham, who posted online a picture of herself and husband Owain Walbyoff in their wedding finery.
So why didn't Kate attend. And is it all down to the Middleton Rules?
Close friends insist Kate's critics are cruelly ignoring the sheer exhaustion of managing toddler George - who hit the terrible twos in July - and his baby sister.
It is also quite possible that the Duchess is still breastfeeding 16-week-old Charlotte and was therefore unwilling to interrupt her routine by having to fit the nursing schedule around a wedding that would have meant a 650-mile round-trip.
Like many mothers, she has found breastfeeding at times difficult and tiring - that was especially the case with George. Consider, too, the fact that had she attended, much of the spotlight would have been on her and not the bride, and one begins to understand why she decided to stay away to avoid the hullabaloo.
What is harder to work out is William's presence. To put it bluntly: why is he partying with Pippa and not helping out his wife at home?
His new job as a helicopter pilot with the East Anglian Air Ambulance service involves working "four days on, four days off". This means the larger part of last week's break was spent not with Kate and his family, but at or travelling to and from the wedding, a six-hour drive from Anmer Hall, their home near Sandringham.
Friends say Kate was entirely relaxed about William using up so much of his off-duty time away from home. "She knows how to handle him and she lets him have his head from time to time to blow off steam," says one of her loyal circle. "And remember, her sister was there, too."
It is worth recalling that in his 20s, William certainly liked "blowing off steam" - or getting "trashed" as his friends put it - from time to time.
But now he's 33 and a father of two, many would say those days should be behind him. Certainly there has been a dramatic reduction in the number of social events the couple have graced.
In the two years leading up to their engagement, Kate and William went to umpteen weddings together.
But she attended none in the two years after they married and is thought to have been to only three since - the wedding in 2013 of polo player Mark Tomlinson to Olympic horsewoman Laura Bechtolsheimer in the Swiss resort of Arosa; that of the Prince's long-time friend William van Cutsem to Rosie Ruck Keene (William's old flame); and that of friends Tom Eaves and Libby Keir in London last year.
Last weekend's Maclean nuptials had clearly been prioritised in William's diary, even though they clashed with the VJ-Day ceremony in London, where other senior royals were on parade.
The Queen has got used to William missing some important ceremonial events since his marriage and has generally been willing to tolerate these absences (and Kate's virtual invisibility) out of deference to their family life and the Prince's day job.
It didn't stop senior courtiers, who do not like contrasting images of duty and pleasure - especially on occasions of national commemoration - grumbling about the Prince heading to Devon for the wedding of a socialite and an estate agent.
In fact, not only did he attend the wedding, he was also at the stag party, which included a trip to Newmarket races.
To be fair, William has scaled back on his social life since he became a husband. But he has also been to at least five weddings on his own, including that of old friend Tom van Straubenzee, when he was reported to have chipped a tooth at the reception.
Some claim that after starting a family and particularly since the arrival of Charlotte, Kate has been discouraging William from accepting too many social engagements.
If it is true - as reported last week - that friends have been complaining they haven't seen William "for ages", then there are echoes of the troubled times of Charles and Diana.
Fed up that Charles wanted to continue leading a bachelor lifestyle even after the arrival of William and Harry, Diana put her foot down, and many of his oldest friends found themselves off the Highgrove guest list.
Of course, there is absolutely no suggestion that - unlike his parents' doomed marriage - William's relationship with Kate is anything but very happy.
But I understand there are some issues that are concerning Palace aides as Kate has, at times, struggled to adapt to royal life. In particular, she loathes the constant comparisons with Diana - especially when these emanate from within Palace walls.
Living up to the public image of the late Princess, let alone William's near veneration of his mother, has proved a significant strain at times. Indeed, I am told it has even been murmured that when the time comes, she might not want to be Princess of Wales at all - which could mean the title has gone for ever.
She also dislikes references to her as a clothes horse. Friends say that while she is naturally image-conscious, she is certainly not a fashion obsessive. (And Diana, incidentally, also tired of being defined by her wardrobe - eventually instructing Buckingham Palace to cease issuing the names of the designers of her clothes she wore on public engagements.)
There is considerable sympathy from the Queen, who understands what a daunting role the Duchess has and feels that on those public appearances she does make, Kate has acquitted herself well.
Her one reservation has been that Kate was clinging too much to her family. Despite being based mainly in Norfolk, she does still frequently return to Bucklebury, the Middleton family home in Berkshire.
Royal aides may privately complain about the proximity of the entire Middleton clan - mother Carole, father Michael, as well as Pippa and brother James - in the Cambridges' life, but have had to accept that this situation has come about not because of Kate, but because it is William's choice.
No in-laws have been as close to the Royal Family as the Middletons. The Spencer family played no part in Diana's life after her marriage nor did the Fergusons after the Duchess of York wed Prince Andrew.
And we rarely heard of the Rhys-Joneses after their daughter Sophie married Prince Edward, and never of the Laurences after their naval officer son Tim wed the Princess Royal.
All the same, there was, significantly, no invitation for the Middletons to join the Queen's Windsor Castle house party and carriage procession for Royal Ascot in June.
And at Charlotte's christening last month they went by car to church at Sandringham like the other guests, rather than walking with William and Kate.
One reason why Kate has relied so much on her parents is because there has been no one on the Windsor side to guide her through the royal maze.
The Duke and Duchess's court are also outsiders in many ways, and they have missed the perceptive presence of William's former private secretary Jamie Lowther-Pinkerton, a former SAS officer, who stepped down from the full-time role two years ago.
Some say the reason why William was happy to relocate to the countryside was partly because Kate still finds it uncomfortable to be in the presence of other royals and the stiff formality of their palaces. Who can blame her?
Cutting remarks said to have emanated from courtiers about her hair, her heels and her hemlines have also not gone unnoted.
Some complaints have struck home and there have been subtle adjustments to her wardrobe after criticism she was showing too much leg - and the Queen is said to have an aversion to her wedge-heeled shoes.
But on her hair - her crowning glory, if you like - Kate is resolutely stubborn, refusing to cut it despite comments that it is too glossy and has become too much of a distraction.
There remains, too, one other source of friction - the relationship between the couple and William's father, Prince Charles.
They were hugely irritated by the leaking of suggestions that they were denying Charles access to his grandson George and that the Middletons were the number one grandparents.
A close friend of William tells me: "The problem is the Prince of Wales is so sensitive to any reproach and anything that he feels undermines his position.
"The fact is Charles can't cope with the disorder that naturally comes with a very lively toddler like George. Mike Middleton, on the other hand, rather enjoys it."
Such an attitude goes some way to explain why when it came to finding a country home, William chose not to settle near his father in Gloucestershire, but rather in Norfolk.
All the same, by wrapping Kate in cotton wool at Anmer, William is in danger of presenting his wife as something of a recluse.
To the public, however, Kate remains a much-loved member of the Royal Family and one who has contributed enormously to its popularity.
They look forward to the time when she takes a more prominent role on the royal stage, and if that currently means she chooses to keep a lower profile by avoiding the weddings of old friends, then they will not mind one bit.
- Daily Mail UK.