diff --git a/htmlcheck/checker.go b/htmlcheck/checker.go
index 6ee15b4..330f195 100644
--- a/htmlcheck/checker.go
+++ b/htmlcheck/checker.go
@@ -27,3 +27,11 @@ type HTMLChecker interface {
 }
 
 // var NotYetFinished = errors.New("the HTML checker has not yet been finished")
+
+type htmlCheckerBackend interface {
+	getCheckerAttrValue(string) string
+	sendTagMessage(string)
+	getCheckerContextValue(string) any
+	addExternalRef(*url.URL)
+	addInternalRef(string)
+}
diff --git a/htmlcheck/tags.go b/htmlcheck/tags.go
new file mode 100644
index 0000000..6c37524
--- /dev/null
+++ b/htmlcheck/tags.go
@@ -0,0 +1,205 @@
+/*
+ * Amsterdam Web Communities System
+ * Copyright (c) 2025 Erbosoft Metaverse Design Solutions, All Rights Reserved
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+// The htmlcheck package contains the HTML Checker.
+package htmlcheck
+
+import (
+	"fmt"
+	"net/url"
+	"regexp"
+	"strings"
+)
+
+type causeLineBreakFunc func(*tag, bool) bool
+type closingTagFunc func(*tag) string
+type rewriteContentsFunc func(*tag, string, bool, htmlCheckerBackend) string
+
+type tag struct {
+	name        string
+	index       int
+	lineBreak   bool
+	allowClose  bool
+	balanceTags bool
+	clb         causeLineBreakFunc
+	ct          closingTagFunc
+	rwc         rewriteContentsFunc
+}
+
+func (t *tag) causeLineBreak(isClosing bool) bool {
+	if t.clb == nil {
+		return t.lineBreak
+	}
+	return t.clb(t, isClosing)
+}
+
+func (t *tag) makeClosingTag() string {
+	if t.ct == nil {
+		return ""
+	}
+	return t.ct(t)
+}
+
+func (t *tag) rewriteContents(contents string, isClosing bool, ctxt htmlCheckerBackend) string {
+	if t.rwc == nil {
+		return contents
+	}
+	return t.rwc(t, contents, isClosing, ctxt)
+}
+
+func createSimpleTag(name string, brk bool) *tag {
+	return &tag{
+		name:        strings.ToUpper(name),
+		index:       -1,
+		lineBreak:   brk,
+		allowClose:  false,
+		balanceTags: false,
+		clb:         nil,
+		ct:          nil,
+		rwc:         nil,
+	}
+}
+
+func createWBRTag() *tag {
+	return &tag{
+		name:        "WBR",
+		index:       -1,
+		lineBreak:   false,
+		allowClose:  false,
+		balanceTags: false,
+		clb:         nil,
+		ct:          nil,
+		rwc: func(t *tag, contents string, isClosing bool, ctxt htmlCheckerBackend) string {
+			ctxt.sendTagMessage("WBR")
+			return contents
+		},
+	}
+}
+
+func stdClosingTag(tag *tag) string {
+	return fmt.Sprintf("</%s>", tag.name)
+}
+
+func createOpenCloseTag(name string, brk bool) *tag {
+	return &tag{
+		name:        strings.ToUpper(name),
+		index:       -1,
+		lineBreak:   brk,
+		allowClose:  true,
+		balanceTags: false,
+		clb:         nil,
+		ct:          stdClosingTag,
+		rwc:         nil,
+	}
+}
+
+func createListElementTag(name string) *tag {
+	return &tag{
+		name:        strings.ToUpper(name),
+		index:       -1,
+		lineBreak:   true,
+		allowClose:  true,
+		balanceTags: false,
+		clb: func(t *tag, isClosing bool) bool {
+			return !isClosing
+		},
+		ct:  stdClosingTag,
+		rwc: nil,
+	}
+}
+
+func createBalancedTag(name string, brk bool) *tag {
+	return &tag{
+		name:        strings.ToUpper(name),
+		index:       -1,
+		lineBreak:   brk,
+		allowClose:  true,
+		balanceTags: true,
+		clb:         nil,
+		ct:          stdClosingTag,
+		rwc:         nil,
+	}
+}
+
+func createNOBRTag() *tag {
+	return &tag{
+		name:        "NOBR",
+		index:       -1,
+		lineBreak:   false,
+		allowClose:  true,
+		balanceTags: true,
+		clb:         nil,
+		ct:          stdClosingTag,
+		rwc: func(t *tag, contents string, isClosing bool, ctxt htmlCheckerBackend) string {
+			if isClosing {
+				ctxt.sendTagMessage("/NOBR")
+			} else {
+				ctxt.sendTagMessage("NOBR")
+			}
+			return contents
+		},
+	}
+}
+
+var hrefPattern = regexp.MustCompile(`(?i:href\s*=)`)
+var targetPattern = regexp.MustCompile(`(?i:target\s*=)`)
+
+func extractAttribute(s string) string {
+	s = strings.TrimSpace(s)
+	if s[0] == '\'' || s[0] == '"' {
+		p := strings.IndexByte(s[1:], s[0])
+		if p < 0 {
+			return ""
+		}
+		return s[1 : p+1]
+	}
+	return strings.Fields(s)[0]
+}
+
+func rewriteATagContents(t *tag, contents string, isClosing bool, ctxt htmlCheckerBackend) string {
+	if isClosing {
+		return contents // don't bother checking close tag
+	}
+	bounds := hrefPattern.FindStringIndex(contents)
+	if bounds != nil {
+		s := extractAttribute(contents[bounds[1]:])
+		if s != "" && (strings.HasPrefix(s, "http:") || strings.HasPrefix(s, "https:")) {
+			ref, err := url.Parse(s)
+			if err != nil {
+				ctxt.addExternalRef(ref)
+			}
+		}
+	}
+
+	targetSeen := false
+	bounds = targetPattern.FindStringIndex(contents)
+	if bounds != nil {
+		s := extractAttribute(contents[bounds[1]:])
+		if s != "" {
+			targetSeen = true
+		}
+	}
+	if targetSeen {
+		return contents
+	}
+	tail := ctxt.getCheckerAttrValue("ANCHORTAIL")
+	return contents + " " + tail
+}
+
+func createATag() *tag {
+	return &tag{
+		name:        "A",
+		index:       -1,
+		lineBreak:   false,
+		allowClose:  true,
+		balanceTags: true,
+		clb:         nil,
+		ct:          stdClosingTag,
+		rwc:         rewriteATagContents,
+	}
+}