Even though ij often fills a single square in puzzle, it is not a character in the Dutch alphabet. It is sometimes incorrectly assumed to be in place of y (y is only used for foreign words). It is a combination of i and j, but has special uppercasing rules in that they are uppercased together; e.g. IJzer (iron). There's even a Unicode codepoint assigned as well: ij (U+0133 LATIN SMALL LIGATURE IJ), although its use is discouraged.

See also: https://en.wikipedia.org/wiki/IJ_(digraph) and https://nl.wikipedia.org/wiki/IJ_(digraaf).

Some people are really inconsistent about this, insisting it's a single letter, despite it not having a place in the alphabet. Some do try to give it a place in the alphabet in place of the 'y', or before or after it but still insisting there's only 26 letters in the alphabet.

It's really a digraph, a phoneme made out of two characters. But it's an inconsistent digraph in that both characters are capitalised together, whereas with other digraphs, only the first is capitalised.

It's not entirely true that 'y' is only used in foreign words. It's used in import words that have been part of the Dutch language for a very long time now. 'Royaal' and 'symbool' are not spelled like that in any neighbouring language, so they've been thoroughly Dutchified over the centuries. They're not foreign anymore.

> There's even a Unicode codepoint assigned as well: ij (U+0133 LATIN SMALL LIGATURE IJ)

And that codepoint was actually massively helpful to represent the ij-as-single-letter in the practice application: https://lingo.vincenttunru.com

A few months ago, someone tried to register her newborn in Brussels (which is officially a bilingual city: Dutch and French) with a name starting with IJ, and had a very hard time convincing the French speaking civil servants that both characters had to be capitalized: https://www.bruzz.be/samenleving/geboorteaangifte-brussel-st...

Its not in the alphabet tho