Before the arrival of Mac OS X, our Macs had remained almost free from the property lists and other XML files that now seem to fill them. Those owe their origin to the grandfather of markup languages, SGML, originally known as Generalised Markup Language. That was invented by Charles Goldfarb, Ed Mosher and Ray Lorie in 1969, when they were working at IBM, as a means of structuring text semantically, and first used a different form of markup, as in
:h1.Chapter 1: Introduction
to set that text as a top-level headline. Ordered lists should look familiar to anyone who writes HTML:
:ol
:li.Item one.
:li.Item two.
:eol.
SGML was flexible as to markup formatting, but has become most widely seen using the angle brackets <> common to HTML, XML, and other markup languages.

Although it has never been popular in its own right, SGML still features in some products where markup is required to impart structure and meaning.

FrameMaker, originally developed by Frame Technology, is a high-end technical publishing system bought by Adobe in 1995. It was then offered in a premium version with extensive support for SGML, seen here in 2002, two years before Adobe dropped this Mac version.

XML

In 1996, a working group of W3C (the World Wide Web Consortium) started developing a profile of SGML that became known as Extended Markup Language, or XML. Work continued through 1997, and in February 1998 XML 1.0 was adopted as a W3C Recommendation. While there’s also a slightly different version 1.1, published in 2004, and various editions of 1.0, in its fundamentals the XML we use today is still version 1.0, with 1.1 only recommended for special purposes.

Property lists

Unlike traditional implementations of Unix, NeXTSTEP used its own property lists to contain serialised objects including settings. When Mac OS X was introduced, those were replaced by a new XML format using a public Document Type Declaration (DTD) still used today.

Although intended to be expressed in plain text, binary representations of XML developed during the early years of the new millennium, and Apple decided to adopt its own, bplist, in the early days of Mac OS X. This brought improved parsing speed, as well as being more compact, and has acted as a deterrent to those who might make casual changes to critical property lists. These were introduced in Mac OS X 10.2 Jaguar in 2002, and have been used as standard for property lists since Mac OS X 10.4. They are described well in this Wikipedia article.

A typical modern property list coded in XML might read
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
<date>2017-10-10T13:13:43Z</date>
</array>
</plist>
That specifies a datestamp in an extended attribute.

Tools

Bundled tools to create and edit property lists have remained disappointingly primitive, but there has been no shortage of contenders from third parties.

This is the ElfData XML Editor, one of the first to be released in 2001, seen two years later in Mac OS X 10.2 Jaguar editing DocBook XML format.

In 2004, David Reitter created a version of GNU Emacs with an Aqua interface and named it Aquamacs. It’s seen here in 2006, in Mac OS X 10.4 Tiger, with its XML tools for editing a property list.

Another early entrant, from 2002, that has blossomed into one of the most extensive and sophisticated XML development environments is cross-platform Oxygen, from SyncRO Soft. Although written in Java its Mac versions have been sensitively implemented. It’s seen here in Mac OS X 10.4 Tiger in 2006, viewing an XML rendition of Shakespeare’s Hamlet.

This is Syntext Serna in 2007, again in Mac OS X 10.4 Tiger, seen editing an XML version of my PhD thesis that had originally been written in Adobe FrameMaker+SGML.

Other editors came and went, such as XML Editor, here in the last few days of Mac OS X 10.4 Tiger in 2007. This is a table from my thesis.

Major text editors also gained XML powers. These are Safari’s preferences in Mac OS X 10.5 Leopard, seen rendered by Rich Siegel’s BBEdit. He first distributed this text editor for System 6 back in 1992, and over 30 years later it remains one of the few high-end text editors for macOS.

My final example returns to the specialist features in Oxygen, seen here in Mac OS X 10.7 Lion in 2012, where it’s being used with a botanical flora.

Today XML and property lists remain at the heart of macOS, something I doubt that Charles Goldfarb ever dreamed of back in 1969.

References

Charles F Goldfarb (1996) The Roots of SGML – A Personal Recollection, Wayback Machine
SGML on Wikipedia
XML on Wikipedia
Property lists on Wikipedia