feat(removeUnknownAndDefaults): apply to xml declarations (#1872)

docs/03-plugins/remove-unknowns-and-defaults.mdx

@@ -13,6 +13,9 @@ svgo:
     defaultAttrs:
       description: If to remove attributes that are assigned their default value anyway.
       default: true
+    defaultMarkupDeclarations:
+      description: If to remove XML declarations that are assigned their default value. XML declarations are the properties in the <code>&lt;?xml … ?&gt;</code> block at the top of the document.
+      default: true
     uselessOverrides:
       description: If to remove attributes that are being if the same value is being inherited by it's parent element anyway.
       default: true
@@ -29,6 +32,8 @@ svgo:
 
 Removes unknown elements and attributes, as well as attributes that are set to their default value.
 
+This can also remove defaults from the XML declaration if present in the document, namely [`standalone`](https://www.w3.org/TR/REC-xml/#sec-rmd) if it's set to `no`.
+
 ## Usage
 
 <PluginUsage/>

docs/03-plugins/remove-xml-proc-inst.mdx

@@ -17,7 +17,7 @@ An XML declaration is the line at the top of an XML file to indicate document me
 
 The XML declaration is optional in [XML 1.0](https://www.w3.org/TR/REC-xml/#sec-prolog-dtd), but mandatory in the [XML 1.1](https://www.w3.org/TR/2006/REC-xml11-20060816/#sec-prolog-dtd). If the XML declaration is omitted, the document is assumed to follow the XML 1.0 specifications, which won't impact SVG documents.
 
-It can be safely removed without impacting compatibility.
+It can be safely removed without impacting compatibility with SVG clients. However, some tools may fail to detect the MIME-type as `image/svg+xml` if this is removed.
 
 ## Usage
 

plugins/plugins-types.d.ts

@@ -14,8 +14,8 @@ type DefaultPlugins = {
   cleanupIds: {
     remove?: boolean;
     minify?: boolean;
-    preserve?: Array<string>;
-    preservePrefixes?: Array<string>;
+    preserve?: string[];
+    preservePrefixes?: string[];
     force?: boolean;
   };
   cleanupNumericValues: {
@@ -146,7 +146,7 @@ type DefaultPlugins = {
   };
   removeDoctype: void;
   removeEditorsNSData: {
-    additionalNamespaces?: Array<string>;
+    additionalNamespaces?: string[];
   };
   removeEmptyAttrs: void;
   removeEmptyContainers: void;
@@ -179,6 +179,12 @@ type DefaultPlugins = {
     unknownContent?: boolean;
     unknownAttrs?: boolean;
     defaultAttrs?: boolean;
+    /**
+     * If to remove XML declarations that are assigned their default value. XML
+     * declarations are the properties in the `<?xml … ?>` block at the top of
+     * the document.
+     */
+    defaultMarkupDeclarations?: boolean;
     uselessOverrides?: boolean;
     keepDataAttrs?: boolean;
     keepAriaAttrs?: boolean;
@@ -194,7 +200,7 @@ type DefaultPlugins = {
   removeViewBox: void;
   removeXMLProcInst: void;
   sortAttrs: {
-    order?: Array<string>;
+    order?: string[];
     xmlnsOrder?: 'front' | 'alphabetical';
   };
   sortDefsChildren: void;
@@ -262,17 +268,17 @@ export type BuiltinsWithRequiredParams = {
   };
   addClassesToSVGElement: {
     className?: string;
-    classNames?: Array<string>;
+    classNames?: string[];
   };
   removeAttributesBySelector: any;
   removeAttrs: {
     elemSeparator?: string;
     preserveCurrentColor?: boolean;
-    attrs: string | Array<string>;
+    attrs: string | string[];
   };
   removeElementsByAttr: {
-    id?: string | Array<string>;
-    class?: string | Array<string>;
+    id?: string | string[];
+    class?: string | string[];
   };
 };
 

plugins/removeUnknownsAndDefaults.js

@@ -99,6 +99,7 @@ exports.fn = (root, params) => {
     unknownContent = true,
     unknownAttrs = true,
     defaultAttrs = true,
+    defaultMarkupDeclarations = true,
     uselessOverrides = true,
     keepDataAttrs = true,
     keepAriaAttrs = true,
@@ -107,6 +108,13 @@ exports.fn = (root, params) => {
   const stylesheet = collectStylesheet(root);
 
   return {
+    instruction: {
+      enter: (node) => {
+        if (defaultMarkupDeclarations) {
+          node.value = node.value.replace(/\s*standalone\s*=\s*(["'])no\1/, '');
+        }
+      },
+    },
     element: {
       enter: (node, parentNode) => {
         // skip namespaced elements