elementui样式库分析——alert

/* BEM
 -------------------------- */

/**
  插值
  套一层class="el-.."
  在一个选择器内声明变量（如：$B、$E），嵌套在里面的其他选择器都可以访问到它
*/
@mixin b($block) {
  $B: $namespace+‘-‘+$block !global;

  .#{$B} {
    @content;
  }
}

/**
  插值
  套一层class="el-title__..."
  at-root:输出到根层级上
*/
@mixin e($element) {
  $E: $element !global;
  $selector: &;
  $currentSelector: "";
  @each $unit in $element {
    $currentSelector: #{$currentSelector + "." + $B + $element-separator + $unit + ","};
  }

  @if hitAllSpecialNestRule($selector) {
    @at-root {
      #{$selector} {
        #{$currentSelector} {
          @content;
        }
      }
    }
  } @else {
    @at-root {
      #{$currentSelector} {
        @content;
      }
    }
  }
}
/**
  插值
  套一层class="...__content"
*/
@mixin m($modifier) {
  $selector: &;
  $currentSelector: "";
  @each $unit in $modifier {
    $currentSelector: #{$currentSelector + & + $modifier-separator + $unit + ","};
  }

  @at-root {
    #{$currentSelector} {
      @content;
    }
  }
}