Commit e981b090 authored by Taddeüs Kroes's avatar Taddeüs Kroes

Updated README

parent 0f0ddfed
......@@ -42,6 +42,9 @@ util.cmx simple.cmx: color_names.cmx
stringify.cmx parser.cmx simple.cmx shorthand.cmx: util.cmi
$(addsuffix .cmx,$(MODULES)): $(addsuffix .cmi,$(PRE_TGTS))
markdown $^ > $@
rm -f *.cmi *.cmx *.o parser.mli parser.conflicts \
parser.automaton $(RESULT)
parser.automaton README.html $(RESULT)
mincss is an extendible CSS minifier written in OCaml. It contains a complete
parser for the CSS3 language, along with consistent type definitions and a
traversal utility function for use in transformation passes.
mincss is currently still in development, finished components are the parser,
stringification (along with whitespace compression), and color compression.
Rulset merging is partially documented below but currently unimplemented.
mincss is an extendible CSS minifier written in OCaml. It features a complete
parser for the CSS3 language, along with type definitions that are consistent
with the official CSS specification and a traversal utility function for use in
transformation passes.
- Whitespace compression
- Color compression
- Creation of shorthand properties (e.g. `font` and `background`)
- Ruleset merging (see below)
- Command-line interface and web interface
Whitespace compression
Ruleset merging
a, | a,.myclass [class~="foo"]>p{color:#fff}
.myclass [class ~= "foo"] > p { |
color: #fff; |
} |
Apart from simply writing the CSS in a shorter format (i.e.
whitespace/color/shorthand compression), mincss attempts to restructure rule
sets such that the resulting stylesheet is the minimal representation of the
input. For example:
Compression of simple expressions
a { color: red }
p { color: red }
color: white; | color: #fff;
font-weight: normal; | font-weight: 400;
can be written much shorter as:
Generation of shorthand properties
a, p { color: red }
font-weight: normal; | font: normal 12px/15px sans-serif;
font-size: 12px; |
line-height: 15px; |
font-family: sans-serif; |
Merging selectors is something that is done by the programmer in most cases,
but the example above may occur when multiple different CSS files are merged
into one, or when a large CSS file is structured in such a way that the
definitions of `a` and `p` are far apart. Another thing that may happen is that
some framework file defines a default style for a selector, that is then
overwritten in a custom stylesheet, for example:
Any existing shorthands are first unfolded into their non-shorthand
counterparts, after which the last value is used for shorthand generation:
/* file: framework.css */
a {
border: 1px solid red;
font: normal 12px/15px sans-serif; | font: bold 12px/15px sans-serif;
font-weight: bold; |
/* file: my-special-page.css */
a {
border-color: blue;
Command-line interface
Output of `mincss -h`:
which can be merged into:
Usage: ./mincss [<options>] [<file> ...]
a {
border: 1px solid blue;
Generic options:
-h, --help Show this help message
-v, --verbose Verbose mode: show compression rate
-o <file> Output file (defaults to stdout)
<file> ... Input files (default is to read from stdin)
Optimization flags (if none are specified, all are enabled):
-w, --whitespace Eliminate unnecessary whitespaces (has the greatest effect, omit for pretty-printing)
-c, --simple Shorten colors and font weights
-s, --shorthands Generate shorthand properties
-d, --duplicates Prune duplicate properties (WARNING: may affect cross-browser hacks)
-p, --pretty Shorthand for -c -s -d
-e, --echo Just parse and pretty-print, no optimizations
Compression phases
To achieve the features listed above, the input stylesheet is rewritten in a
number of steps:
1. Parse the input CSS, producing an Abstract Syntax Tree (AST) in accordance
with the CSS syntax definition. This eliminates unnecessary whitespaces and
catches syntax errors.
2. Transform shorthand declarations into a separate declaration for each
expression in the shorthand.
3. Duplicate rulesets for each of its selectors, so that every ruleset has
exactly one selector.
4. Create a new declaration block for each property declaration on each
selector, e.g. `a,p{color:red;border:blue}` becomes `a{color:red}
a{border:blue} p{color:red} p{border:blue}`.
5. Prune duplicate declarations (when the same property is overwritten for the
same selector). Note: this may be disabled with `--no-prune` for stylesheets
that contain duplication hacks.
6. Combine selectors for identical blocks (as long as the correct order of
declarations is preserved).
7. Concatenate blocks for identical (combinations of) selectors.
8. Optimize individual declaration blocks by generating shorthand declarations
and simple compression on expressions (i.e. color compression, removal of
unnecessary string quotes, etc.).
9. Output the resulting AST with minimal whitespace.
Formatting options:
--sort Sort declarations in each selector group
Building mincss
Dependencies are [OCaml]( 4.0 and
Compression scores
Bootstrapping on a Debian system can be done as follows:
TODO: compare to existing minifiers
$ sudo apt-get install ocaml opam git
$ opam init
$ opam switch 4.01.0
$ opam install menhir
$ git clone
$ cd mincss
$ make
$ ./mincss --help
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