diff --git a/core/modules/config.js b/core/modules/config.js
index 9f5f7a78e..9d9dd3376 100644
--- a/core/modules/config.js
+++ b/core/modules/config.js
@@ -38,15 +38,16 @@ exports.htmlBlockElements = "address,article,aside,audio,blockquote,canvas,dd,de
 
 exports.htmlUnsafeElements = "script".split(",");
 
-// See: https://html.spec.whatwg.org/#valid-custom-element-name
+// Custom Web Components: https://html.spec.whatwg.org/#valid-custom-element-name
 exports.htmlForbiddenTags = "annotation-xml,color-profile,font-face,font-face-src,font-face-uri,font-face-format,font-face-name,missing-glyph".split(",");
 
+// (EBNF notation) - PotentialCustomElementName ::= [a-z] (PCENChar)* '-' (PCENChar)*
 // Unicode table with ranges see: https://symbl.cc/en/unicode-table
-// The "prefix" is obligatory!
 exports.htmlCustomPrimitives = {
 	prefix: "[a-z]",
 	validPCENChar: ".|[0-9]|_|[a-z]|\xB7|[\xC0-\xD6]|[\xD8-\xF6]|[\u00F8-\u037D]|[\u037F-\u1FFF]|[\u200C-\u200D]|[\u203F-\u2040]|[\u2070-\u218F]|[\u2C00-\u2FEF]|[\u3001-\uD7FF]|[\uF900-\uFDCF]|[\uFDF0-\uFFFD]",
-	nonValidPCENChar: "[\x00-\x2C]|\x2F|[\x3A-\x40]|[\x5B-\x60]|[\x7B-\xB6]|[\xB8-\xBF]|\xD7|\xF7|\x37E|[\u2000\u200B]|[\u200E-\u203E]|[\u2041-\u206F]|[\u2190-\u2BFF]|[\u2FF0-\u3000]|[\uD800-\uF8FF]|[\uFDD0-\uFDEF]|[\uFFFE-\uFFFF]"
-};
+	sanitizePCENChar: "[\x00-\x2C]|\x2F|[\x3A-\x40]|[\x5B-\x60]|[\x7B-\xB6]|[\xB8-\xBF]|\xD7|\xF7|\x37E|[\u2000\u200B]|[\u200E-\u203E]|[\u2041-\u206F]|[\u2190-\u2BFF]|[\u2FF0-\u3000]|[\uD800-\uF8FF]|[\uFDD0-\uFDEF]|[\uFFFE-\uFFFF]"
+	};
+exports.htmlCustomPrimitives.nonValidPCENChar = "[A-Z]|" + exports.htmlCustomPrimitives.sanitizePCENChar;
 
 })();
diff --git a/core/modules/utils/dom/dom.js b/core/modules/utils/dom/dom.js
index f8f779582..ac41b528d 100644
--- a/core/modules/utils/dom/dom.js
+++ b/core/modules/utils/dom/dom.js
@@ -387,56 +387,44 @@ exports.querySelectorAllSafe = function(selector,baseElement) {
 };
 
 /*
-Make sure HTML tag names are valid
+Sanitize HTML tag- and custom web component names
 	1. Check the string, if it is a valid html tag - using this spec: https://html.spec.whatwg.org/#syntax-tag-name
-		1.1 Tag names are "case-insensitive"
+		1.1 Tag names are "case insensitive"
     2. Extend 1. and allow hyphens: "-"
-		2.1 Browsers allow "AA-AA", so do we
-		2.2 AA-AA cannot be used for styling
-		2.3 aa-aa can be used for styling
+		2.1 Browsers allow "AA-AA", so do we. Be aware there may be styling problems
 
-    3. Implement a forbidden list according to https://html.spec.whatwg.org/#valid-custom-element-name
-		3.1 exports.htmlForbiddenTags = "annotation-xml,color-profile,font-face,font-face-src,font-face-uri,font-face-format,font-face-name,missing-glyph".split(",");
-
-	4. If 1., 2. and 3. pass return the HTML tag as a valid tag -- That should be fast and cover 90% of html tags users will use.
-
-    5. If 4. does not match, we check for invalid character ranges up to \uFFFF. So we can detect problems in a range JS RegExp can handle.
-    6. We assume that everything out of js RegExp-range is valid, which would be OK for \u10000-\uEFFFF according to the spec.
+	3. Sanitize input parameters - spec: https://html.spec.whatwg.org/#valid-custom-element-name
+    4. Implement a forbidden list: exports.htmlForbiddenTags - see: $:/core/modules/config.js
+    5. Check function parameters for invalid character ranges up to \uFFFF. This detects problems in a range JS RegExp can handle
+    6. We assume that everything out of js RegExp-range is valid, which is OK for \u10000-\uEFFFF according to the spec
 
+	Unicode overview: https://symbl.cc/en/unicode-table/
 */
 exports.makeTagNameSafe = function(tag,defaultTag) {
-	defaultTag = defaultTag || "SPAN";
-	var result = defaultTag;
+	// Custom web-components need to be "lowercase()"
+	var regxSanitizeChars = new RegExp($tw.config.htmlCustomPrimitives.sanitizePCENChar,"mg");
+	// Sanitize inputs to make the logic simple
+	defaultTag = (defaultTag) ? defaultTag.replace(regxSanitizeChars,"") : "SPAN";
+	tag = (tag) ? tag.replace(regxSanitizeChars,"") : defaultTag;
 
-	// RegExp for valid standard HTML element, extended with hyphen "-"
-	var regexValidTag = /(?:[a-z]|[A-Z]|[0-9]|-)+/g;
+	// RegExp for valid standard HTML element, extended including hyphen "-"
+	var regexStandardChars = /(?:[a-z]|[A-Z]|[0-9]|-)+/g,
+		result = "";
 
-	// Custom web-components must to be "lowercase()"
-	var regxInvalidlTag = new RegExp($tw.config.htmlCustomPrimitives.nonValidPCENChar,"mg");
-
-	// Check if tag matches regexp as a whole
-	if(tag && (tag.match(regexValidTag)[0] === tag)) {
-		result = tag; // valid tag
+	// Check if tag matches standard HTML spec
+	if(tag.match(regexStandardChars)[0] === tag) {
+		result = tag;
 	}
-
-	// Sanitize invalid characters in result
-	if( regxInvalidlTag.exec(result.toLowerCase()) !== null) {
-		result = result.toLowerCase().replace(regxInvalidlTag,"");
+	// Check for unsafe tag and unsafe defaultTag
+	if($tw.config.htmlUnsafeElements.indexOf(result.toLowerCase()) !== -1) {
+		result = ($tw.config.htmlUnsafeElements.indexOf(defaultTag.toLowerCase()) !== -1) ? "safe-" + defaultTag : defaultTag;
 	}
-
-	// Check for unsafe tags
-	if( $tw.config.htmlUnsafeElements.indexOf(result) === -1) {
-		result = "safe-" + result;	
-	}
-
-	// Check for forbidden tag names and log info 
+	// Check for forbidden tag names according to spec and log info to help users
 	if($tw.config.htmlForbiddenTags.indexOf(result.toLowerCase()) >= 0) {
 		console.log("Forbidden custom element:\"" + result.toLowerCase() + "\" See: https://html.spec.whatwg.org/#valid-custom-element-name")
 		result = "safe-" + result;
 	}
-
 	return result;
 };
 
-
 })();
diff --git a/core/modules/widgets/element.js b/core/modules/widgets/element.js
index 534442759..3f8017960 100755
--- a/core/modules/widgets/element.js
+++ b/core/modules/widgets/element.js
@@ -29,15 +29,10 @@ Render this widget into the DOM
 ElementWidget.prototype.render = function(parent,nextSibling) {
 	this.parentDomNode = parent;
 	this.computeAttributes();
-	// Neuter blacklisted elements
+	// Eliminate blacklisted elements
 	this.tag = this.parseTreeNode.tag;
-	this.tag = $tw.utils.makeTagNameSafe(this.tag, "safe" + this.tag);
-	// Restrict tag name to digits, letts and dashes
-
-	// this.tag = this.tag.replace(/[^0-9a-zA-Z\-]/mg,"");
-	
-	// Default to a span
-	this.tag = this.tag || "span";
+	// Sanitize tag name if needed according to Custom Web-Componenets spec
+	this.tag = $tw.utils.makeTagNameSafe(this.tag, "safe-" + this.tag);
 	// Adjust headings by the current base level
 	var headingLevel = ["h1","h2","h3","h4","h5","h6"].indexOf(this.tag);
 	if(headingLevel !== -1) {