Even creative spelling has its rules—and those rules are changing.

For generations, two letters have reigned supreme the realm of creative name spelling: Y and K. Parents replaced workaday vowels with Ys in names from Lynda to Paxtyn, and Cs with Ks in names like Karter and Khloe. The two leading letters coexisted peacefully and shared a common style perspective. They even joined forces in names like Kaytlyn and Kamdyn.

Today, their dominance is threatened. New upstart letter shifts are changing the way America spells its baby names, with a bold, assertive, high-Scrabble-value style. X and Z are the new creative “power letters.”

The torchbearer for the new style is Jaxon, a modern hit that transforms the look of the traditional surname Jackson. At the turn of the turn of the millennium, 9 Jacksons were born for every X-variant of the name (e.g. Jaxon, Jaxxon or Jaxson). Today, the X versions have taken the lead.

The scope of the KS—>X spelling shift has been limited by the shortage of KS names in English. Eight American families did name sons Broox last year, but that’s about the end of the line. For a broader flowering of bold-spelling creativity, look to the letter Z as a sound-alike substitute for a voiced S.

While Z variants of some familiar S names occur in languages like Polish and Portuguese, their use has always been rare in English. Now, Z variants reach into every part of style spectrum. You’ll find the S—>Z shift complementing bold “statement” names (Wizdom), customizing popular contemporary names (Ainzley), and upending the impact of classics (Jamez).

These S—>Z names, a representative sample, were together given to 2000 US babies last year:

X and Z spellings have become so desirable that parents will make additional changes to accommodate the letters, turning a name like Chance into Chantz. X and Z can also be found subbing in for one another in names like Xoe and Zavier, and doubling up in names like Axzel and Alexzandra.

As novel as all of these spellings are, their letter shifts function the same way that I—>Y and C—>K always have. They alter the name’s spelling while leaving its familiar pronunciation intact. The lure of the new shifts is so strong, though, that parents are increasingly using them even when the change affects pronunciation. A solo C, K or S may become an X in a name like Jaxlyn. More often, an unvoiced S (a hissing sound, rather than a buzzing sound) will be replaced by a Z. Such a change requires either a novel pronunciation or a high tolerance for mispronunciations.

Each of these names was given to five or more American babies last year:

Names like Zerenity and Mezziah are dramatic demonstrations of the allure of the power letters. Even when a name’s impact comes from its meaning as a common word, parents will risk obscuring that meaning to secure a Z. In these names, spelling is meaning. Their creativity—or xreativity—speaks volumes.