it seems we could implement it much easier

README.md

@@ -18,7 +18,7 @@ Once the plugin has been installed, it may be you can make your "Stylus" run `xx
 
 1. `1px` will be ignored for experience, you can override it with define your number named `px2rem_ignore_limit`.
 
-2. If you want to preserve px value in some case(html element for example), use `font-size '16px!'`, and also you can override `preserve_px` to '_px'(then `font-size '16_px'`) or something else.
+2. If you want to preserve px value in some case(html element for example), use quote like `font-size '16px'`.
 
 ## Input/Output
 

lib/stylus-px2rem/mixins.styl

@@ -10,11 +10,8 @@ html-font-size ?= 16px;
 style-names ?= "min-height" "max-height" "min-width" "max-width" "width" "height" "border" "margin" "margin-top" "margin-bottom" "margin-left" "margin-right" "padding" "padding-left" "padding-right" "padding-bottom" "padding-top" "line-height"
 // value less then ignore_limit will be ignored and return the original value
 px2rem_ignore_limit ?= 1
-// if you want to preserve px value in some case(html element for example), use `font-size '16px!'`, and also you can override `preserve_px` to '_px'(then `font-size '16_px'`) or something else
-preserve_px ?= 'px!'
 
 px2rem(prop,values){
-    values-px = null;
     values-rem = null;
     need_normalize = !prop in style-names
     for value in values {
@@ -28,10 +25,8 @@ px2rem(prop,values){
                 value-rem = unit(value ,'rem');
             }
             push(values-rem,value-rem)
-        } else if(match(preserve_px+'$',''+value)) {
-            push(values-rem,unquote(replace(preserve_px,px,value)))
-        }  else {
-            push(values-rem,value)
+        } else {
+            push(values-rem,match('px$',''+value) ? unquote(value) : value)
         }
     }
     {prop} : values-rem;