Susy - Compass Plugin 
=====================

Susy is a semantic CSS grid system for designers.

Build beautiful grids of any type, width and breakdown, without touching your
markup or changing the way you work. Built entirely native to
[Compass](http://compass-style.org/), Susy is an expert at fluid grids in an
elastic (or fluid, or fixed) shell that stay where you want without ever
activating that bloody side-scroll bar. Susy sets your width on the outer
element (`container`), adds a `max-width` of `100%` and builds the rest of
your grid in percentages. The philosophy and technique are based on [Natalie
Downe](http://natbat.net/)'s "[CSS
Systems](http://natbat.net/2008/Sep/28/css-systems/)" - which introduces
difficult math in the service of beautiful structure. With the power of
Compass/Sass, Susy will do that math and let you focus on your designs.

Using simple mixins, columns can be created, suffixed, prefixed, and nested -
always in flexible percentages and without touching your markup.

Install 
=======

    sudo gem install compass-susy-plugin

Create a Susy-based Compass Project 
===================================

    compass create <project name> -r susy -u susy

Then edit your `_base.scss`, `_defaults.scss`, `screen.scss` and `print.scss`
files accordingly. A reset is added automatically, and includes support for
HTML5 elements.

Philosophy and Goals
====================

The method comes from [Natalie Downe](http://natbat.net/)'s "[CSS
Systems](http://natbat.net/2008/Sep/28/css-systems/)", but I'll cover it here.

It is important for accessibility and usability that we are:

* Able to control our designs and line-lengths with some amount of precision.

* Responsive to text sizing: In order for our site to be accessible we need to
  allow different font-sizes to be set by the client. In order to maintain
  design integrity of proportions and line-lengths, the grid needs to respond
  to those sizes.

* Responsive to window sizing: In order to maintain usability across
  platforms/monitors, our grid needs to respond to the size of the viewport.
  This is mainly an issue as the viewport shrinks and we are given a
  side-scroll bar. No one likes that. On the large end our design integrity
  and line lengths are more important than taking up all the possible space.

In order to achieve both goals we need to combine the best of the elastic
(em-based) and fluid (%-based) models. The solution is simple: First we build
a fluid grid, then place it inside an elastic shell, and apply a maximum width
to that shell so that it never exceeds the size of the viewport. It's simple
in theory, but daunting in practice, as you constantly have to adjust your
math based on the context.

But Susy harnesses the power of Compass and Sass to do all the math for you.

Grid Basics
===========

* Set up your default grid values (total columns, column width, gutter width,
  side gutter width), your base font size, and important mixins in
  `_base.scss`.
  
    Example:
  
        $base-font-size: 16px;
        $base-line-height: 24px;

        $total-cols: 12; /* a 12-column grid */
        $col-width: 4em; /* each column is 4em (64px) wide */
        $gutter-width: 1em; /* 1em (16px) gutters between columns */
        $side-gutter-width: $gutter-width; /* 1em (16px) padding at the edges of the page as well */

* Set defaults for all the important HTML tags in `_defaults.scss`. It's
  better than using the browser defaults. And better than using ours.

* Create your grid in `screen.scss`: apply the `@include susy` mixin at the
  top level and the `@include container` mixin to the element that contains
  the page grid. This will set up your font sizes, vertical rhythm, and grid
  container.

    Example:

        @include susy;
     
        #page {
          @include container; 
        }
    
    CSS Output:
    
        body {
          font-size: 100%;
          line-height: 1.5em;
        }

        html > body {
          font-size: 16px;
        }

        body {
          text-align: center;
        }

        #page {
          overflow: hidden;
          display: inline-block;
          text-align: left;
          margin-left: auto;
          margin-right: auto;
          width: 61em;
          max-width: 100%;
        }
        #page {
          display: block;
        }

* Use the `@include columns` mixin to declare the width in columns of an
  element, or `@include full` for any element spanning the full width of its
  context.

  There is an important distinction between "root" and "nested" contexts in
  Susy. There is also a distinction between "grid elements" and "non-grid
  elements". Grid elements are any elements that you assign a span to, either
  with the `columns` or `full` mixin. Non-Grid elements include everything
  else. Just as CSS absolute positioning happens in relation to the nearest
  positioned ancestor, Susy grid "context" depends on the nearest grid-element
  ancestor. Any element with the `container` as it's nearest grid ancestor is
  considered to be in the "root" context. Any element within other grid
  elements (with a nearest grid ancestor other than the `container`) is
  considered to be in a "nested" context.
    
  This is important because side-gutters are handled at the root level, as
  margins on root grid elements. Margins that we don't want at nested levels.
  It is also important because Susy grid elements are %-based, and so the
  context is important to Susy's math. `Full` is simply a shortcut to replace
  `columns` when the span should be the full width.
  
    The `columns` mixin:
  
        @include columns($span [, $context]);
  
    The `full` mixin:
  
        @include full([$context]);

  *Note:* Context _must not_ be passed at the root level, and _must_ be passed at nested levels.

* Use `@include alpha` and `@include omega` to declare elements which include
  the first or last column within their parent element.
  
  *Note:* `@include alpha` is _only_ needed in the root level, and does
  nothing in nested contexts. Neither is needed with an `@include full` element.
  
    The `alpha` and `omega` mixins:
    
        @include alpha;
        @include omega([$context]);
  
    Example Scss:
    
        #page {
          @include container;
          header {
            @include full;
            h1 {
              @include full(12);
            }
          }
          nav {
            @include columns(3);
            @include alpha;
          }
          #content {
            @include columns(9);
            @include omega;
            #main {
              @include columns(6,9);
            }
            aside {
              @include columns(3,9);
              @include omega(9);
            }
          }
        }
      
  Susy's CSS output uses floats to arrange the columns, widths to set the
  spans, right-margins to set the getter, and both side margins to set the
  side-gutters on root `alpha` and `omega` elements.

* Use `@include prefix` or `@include suffix` to pad (in columns) the width of
  an element using left and right padding, or `@include pad` to give both `@include
  prefix` and `@include suffix` at once.
  
    The `prefix`, `suffix` and `pad` mixins:
    
        @include prefix($prefix-span [, $context])
        @include prefix($suffix-span [, $context])
        @include pad($prefix-span, $suffix-span [, $context])
  
    Used with `full` these are subtractive, so the full width remains:
    
        header {
          @include full;
          @prefix(2);
        }
    
    Will result in a full-width element, with 2 columns of padding to the left.
    
    Used with `columns` these are addative, so the content width remains:
    
        aside {
          @include columns(3,9);
          @prefix(3,9)
        }
    
    Will result in a 6-column element, with 3 of those columns used as padding 
    on the left.

That's it for the basics! Here's a sample Susy grid layout:

    @include susy;
     
    #page {
      @include container; 
    }
     
    header {
      @include full;
      @include pad(1,1);
      
      h1 {
        @include full(10);
      } 
    }
        
    nav {
      @include columns(3);
      @include alpha;
    }
     
    #content {
      @include columns(9);
      @include omega;
      #main {
        @include columns(6,9);
      }
      aside {
        @include columns(3,9);
        @include omega(9);
      }
    }

Tutorial
========

Being built...

Extra Utility Mixins 
=====================

Extra utilities are included in Susy's `utils.scss` file, with additional list
options, experimental (CSS3/proprietary) CSS, and more.

* `@include show-grid($src)` - Repeat the specified grid image on an element.
  Good for testing your baseline and grid.

* `@include inline-block-list([$horizontalpadding])` - Make list items
  inline-block when floating just won't do the trick (if you need them
  centered or right).

* `@include hide` - Hide content from visual browsers while keeping
  accessability intact.

* `@include skip-link([$top, $right, $bottom, $left])` - Hide a link, and then
  show it again on focus. the TRBL settings allow you to place it absolutely
  on display. Default will be top left of the positioning context.

And then the fun stuff in `_vertical_rhythm.scss`, originally written by Chris
Eppstein and probably moving to the compass core before too long:

* `@include adjust-font-size-to($to_size, [$lines, $from_size])` - adjust the
  font size and number of baseline (line) units to occupy.

* `@include leader([$lines, $font_size, $property])` and `@include
  trailer([$lines, $font_size, $property])` - add leading or trailing
  whitespace to an element. These are added as top and bottom margins (by
  default) that keep your vertical rhythm intact. You can also send "padding"
  as the `$property` or use `@include padding-leader` and `@include
  padding-trailer`. Be aware that this may conflict with uses of
  rhythm-borders.

* `@include leading-border([$width, $lines, $font_size, $style])` and
  `@include trailing-border([$width, $lines, $font_size, $style])` will
  combine border and padding to create borders that also keep the vertical
  rhythm going. The defaults are `1px, 1, $base_font_size, 'solid'`. Also
  available: `@include horizontal-borders` (for both leading and trailing),
  and `@include rhythm-borders` for applying equal borders and padding to all
  sides of a box.


Advanced Options
================

Susy is built for flexibility, so that you always write the code you want to
write. While everything should 'just work' out of the box, there are plenty of
advanced options hidden inside. Here are a few:

* `$hacks` is a boolean constant that you can set in your base.sass file to
  choose between using targeted hacks for IE (a variation of the star hack in
  most cases) in your screen.css, or using a conditional-comment targeted
  ie.css. All the needed mixins are available for either setting. `$hacks` is
  true by default so there is no extra work maintaining multiple files unless
  you want to.

    Example 1:
    
        $hacks: true;
    
        #nav {
          @include inline-block-list;          
        }
    
    Example 2:
    
        $hacks: false;
      
        // in screen.scss
        #nav {
          @include inline-block-list;
        }
        
        //in ie.scss
        #nav li {
         @include ie-inline-block; 
        }

    It requires more maintenance on your part, but the result is a hack-free
    output.
    
     The Susy mixins that use either hacks or targeted mixins are `@include
    omega` (`@include ie-omega([$right-floated: false])`), `@include
    inline-block` (`@include ie-inline-block`), and `@include
    inline-block-list` which sets `@include inline-block` on the list items.
    
     The ie-specific mixins only add the needed ie-specific adjustments, so
    they need to be used in addition to their counterparts, not on their own.

* `gutter($context)` is a function that you can call at any time to return the
  size of a gutter in your given context as a percentage.

    Example:
        
        #nav {
          padding-right: gutter(5);
        }

* `columns($number, $context)` returns the span of `$number` columns in
  `$context` as a percentage. This span includes any gutters between the
  columns spanned.

    Example:
        
        #nav {
          padding-left: columns(3,5);
        }

* `side_gutter()` is also available and takes no arguments since it is always
  used at the top nesting level.

* `$px2em` is a variable that represents the height of one pixel as a fraction
  of your base em-height. Multiply it with your target pixel value to
  represent that value in ems. Note that this is only accurate at your
  `$base_font_size`.

    Example:
    
        #nav {
          border-bottom: {
            style: solid;
            width: $px2em*2px;
          };
        }