What is "+" (+font-face)?

Question

Sass

@include mixin call, but I didn't find "+" in the documentation.
_font face

@mixin font-face($font-family, $file-path, $weight: normal, $style: normal, $asset-pipeline: false )
    @font-face
        font-family: $font-family
        font-weight: $weight
        font-style: $style

        @if $asset-pipeline == true 
            src: font-url('#{$file-path}.eot')
            src: font-url('#{$file-path}.eot?#iefix') format('embedded-opentype'), font-url('#{$file-path}.woff') format('woff'), font-url('#{$file-path}.ttf') format('truetype')
        @else
            src: url('#{$file-path}.eot')
            src: url('#{$file-path}.eot?#iefix') format('embedded-opentype'), url('#{$file-path}.woff') format('woff'), url('#{$file-path}.ttf') format('truetype')

_font

@import "mixins/font-face"

+font-face("raleway", "../fonts/RalewayRegular/RalewayRegular")
+font-face("raleway", "../fonts/RalewayBold/RalewayBold", bold)
+font-face("raleway", "../fonts/RalewayExtraBold/RalewayExtraBold", 800)
+font-face("raleway", "../fonts/RalewayLight/RalewayLight", 300)
+font-face("raleway", "../fonts/RalewaySemiBold/RalewaySemiBold", 600)
+font-face("raleway", "../fonts/RalewayThin/RalewayThin", 100)
+font-face("firasans", "../fonts/FiraSansRegular/FiraSansRegular")

Answer 1

This is the mixin call under SASS syntax (indented):
sass-lang.com/documentation/file.INDENTED_SYNTAX.html