• An AVIF Is an MP4 With One Frame

  XML’s answer to structure was a schema language, a query language, and a namespace system. MP4’s answer is eight bytes, and it turned out to be enough to absorb an entire industry. Every byte in the file lives inside a box, and every box …

• Every XML Feature Is One You Turn Off

  Last post ended on a question. XML is the format in this series that specified everything, so what did all that specifying buy? An answer for every question, and an attack surface made entirely of answers. The other formats in this series …

• Norway Is Not a Boolean

  JSON’s problem is that its specification is too small. It tells you 9007199254740993 is a well-formed number and then declines to say which number. YAML went the other way. The 1.2.2 specification is a book. It has a formal grammar, a …

• Your JSON Parser Disagrees With Mine

  Markdown has too many specs. CSV has one that nobody agreed to follow. JSON is supposed to be the happy ending: a grammar small enough to print on a business card, standardized twice over, and elevated to a full Internet Standard. It is, …

• Nobody Agrees What a CSV Is

  CSV is simple but powerful. Values, separated by commas. It’s easy to understand and use. It is also, by a wide margin, the one that destroys the most data. That’s not a paradox. It’s cause and effect. A format simple enough that everyone …

• Word Documents Used to Be Filesystems

  Last post ended on a promise: a .docx is a ZIP file, and you already know how ZIP works. That’s true, and it’s the smaller half of the story. The interesting part is what .docx replaced, because the old .doc format was doing something …

• ZIP Files Are Read Backwards

  Every format in this series so far reads front to back. PNG starts with a signature and you walk chunks in order. A text file is bytes from the beginning. Markdown parsers scan line by line, top to bottom. ZIP reads backwards. The index is …

• Markdown Is Not a Format, It's an Argument

  I’ve covered PNG and text files, and now it’s time for Markdown, which can be thought of as a philosophy of formatting or a lifestyle of text documents more so than an actually well defined file format. It has structure, and it has …

• There Is No Such Thing as a Text File

  Last time I took apart PNG, which opens with eight bytes whose entire job is to announce “I am a PNG”. A text file opens with nothing. No signature, no header, no length field, no version, no metadata. It is bytes, and then it stops. So …

• How PNG Actually Stores Your Pixels

  I’m starting a series on file formats. Not “here are the ten image formats you should know,” but the actual bytes: what’s in the file, in what order, and why someone decided it should be that way. Starting with PNG, because it’s the format …