Re: Explanation about file property lists.

[dlw at MIT-AI (Daniel L. Weinreb)]

I spoke to KMP and found that the following points probably need to be
cleared up:

File property lists are defined in string-oriented terms.  That is, they
looks like
   "-*-"  "Indicator"  ":"  "Value"  ";"  "Indicator"  ":"  "Value" "-*-"
(in the case of a two-property-long list).  Indicators and Values
are character strings.  They may contain numbers and alphabetic characters
(including hyphen as an alphabetic).  You can also use commas to have several
value strings.  They are just character strings; it
is up to various programs to interpret them.  You can't do computations
with them, they are not Lisp data structure, they do not allow reader-macros,
etc.  They are extremely simple.  That's all there is to them.

The Lisp Machine happens to have a function that opens a file, finds the
property list, and creates a Lisp list corresponding to it, representing
indicators by symbols in the keyword package and so on.  And when it
sees commas in a value, it creates a list.  However, this function
exists only because it is a convenient interface for Lisp programs to
use.  There is nothing implicit in the file property list that has
anything to do with Lisp, at all.