Add SVG namespace auto-detection, custom elements, html: prefix, and fix filter/map tag collision

- Fix filter/map dispatching as HO functions when used as SVG/HTML tags
  (peek at first arg — Keyword means tag call, not function call)
- Add html: prefix escape hatch to force any name to render as an element
- Support custom elements (hyphenated names) per Web Components spec
- SVG/MathML namespace auto-detection: client threads ns param through
  render chain; server uses _svg_context ContextVar so unknown tags
  inside (svg ...) or (math ...) render as elements without enumeration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/static/scripts/sx.js

@@ -627,7 +627,10 @@
       var sf = SPECIAL_FORMS[head.name];
       if (sf) return sf(expr, env);
       var ho = HO_FORMS[head.name];
-      if (ho) return ho(expr, env);
+      if (ho) {
+        // If name is also an HTML tag and first arg is Keyword → not a HO call
+        if (!(HTML_TAGS[head.name] && expr.length > 1 && isKw(expr[1]))) return ho(expr, env);
+      }
 
       // Macro expansion
       if (head.name in env) {
@@ -1056,12 +1059,16 @@
   );
 
   var SVG_NS = "http://www.w3.org/2000/svg";
+  var MATH_NS = "http://www.w3.org/1998/Math/MathML";
 
   /**
    * Render an s-expression to DOM node(s).
    * Returns a DocumentFragment, Element, or Text node.
+   * @param {*} expr - s-expression
+   * @param {Object} env - variable bindings
+   * @param {string|null} ns - namespace URI (SVG_NS or MATH_NS) when inside svg/math
    */
-  function renderDOM(expr, env) {
+  function renderDOM(expr, env, ns) {
     // nil / false → empty
     if (isNil(expr) || expr === false || expr === true) return document.createDocumentFragment();
 
@@ -1079,7 +1086,7 @@
     if (typeof expr === "number") return document.createTextNode(String(expr));
 
     // Symbol → evaluate then render
-    if (isSym(expr)) return renderDOM(sxEval(expr, env), env);
+    if (isSym(expr)) return renderDOM(sxEval(expr, env), env, ns);
 
     // Keyword → text
     if (isKw(expr)) return document.createTextNode(expr.name);
@@ -1093,7 +1100,7 @@
     // List → dispatch
     if (Array.isArray(expr)) {
       if (!expr.length) return document.createDocumentFragment();
-      return renderList(expr, env);
+      return renderList(expr, env, ns);
     }
 
     return document.createTextNode(String(expr));
@@ -1102,34 +1109,34 @@
   /** Render-aware special forms for DOM output. */
   var RENDER_FORMS = {};
 
-  RENDER_FORMS["if"] = function (expr, env) {
+  RENDER_FORMS["if"] = function (expr, env, ns) {
     var cond = sxEval(expr[1], env);
-    if (isSxTruthy(cond)) return renderDOM(expr[2], env);
-    return expr.length > 3 ? renderDOM(expr[3], env) : document.createDocumentFragment();
+    if (isSxTruthy(cond)) return renderDOM(expr[2], env, ns);
+    return expr.length > 3 ? renderDOM(expr[3], env, ns) : document.createDocumentFragment();
   };
 
-  RENDER_FORMS["when"] = function (expr, env) {
+  RENDER_FORMS["when"] = function (expr, env, ns) {
     if (!isSxTruthy(sxEval(expr[1], env))) return document.createDocumentFragment();
     var frag = document.createDocumentFragment();
-    for (var i = 2; i < expr.length; i++) frag.appendChild(renderDOM(expr[i], env));
+    for (var i = 2; i < expr.length; i++) frag.appendChild(renderDOM(expr[i], env, ns));
     return frag;
   };
 
-  RENDER_FORMS["cond"] = function (expr, env) {
+  RENDER_FORMS["cond"] = function (expr, env, ns) {
     var branch = _evalCond(expr.slice(1), env);
-    return branch ? renderDOM(branch, env) : document.createDocumentFragment();
+    return branch ? renderDOM(branch, env, ns) : document.createDocumentFragment();
   };
 
-  RENDER_FORMS["let"] = RENDER_FORMS["let*"] = function (expr, env) {
+  RENDER_FORMS["let"] = RENDER_FORMS["let*"] = function (expr, env, ns) {
     var local = _processBindings(expr[1], env);
     var frag = document.createDocumentFragment();
-    for (var k = 2; k < expr.length; k++) frag.appendChild(renderDOM(expr[k], local));
+    for (var k = 2; k < expr.length; k++) frag.appendChild(renderDOM(expr[k], local, ns));
     return frag;
   };
 
-  RENDER_FORMS["begin"] = RENDER_FORMS["do"] = function (expr, env) {
+  RENDER_FORMS["begin"] = RENDER_FORMS["do"] = function (expr, env, ns) {
     var frag = document.createDocumentFragment();
-    for (var i = 1; i < expr.length; i++) frag.appendChild(renderDOM(expr[i], env));
+    for (var i = 1; i < expr.length; i++) frag.appendChild(renderDOM(expr[i], env, ns));
     return frag;
   };
 
@@ -1140,45 +1147,45 @@
   RENDER_FORMS["defmacro"] = function (expr, env) { sxEval(expr, env); return document.createDocumentFragment(); };
   RENDER_FORMS["defhandler"] = function (expr, env) { sxEval(expr, env); return document.createDocumentFragment(); };
 
-  RENDER_FORMS["map"] = function (expr, env) {
+  RENDER_FORMS["map"] = function (expr, env, ns) {
     var fn = sxEval(expr[1], env), coll = sxEval(expr[2], env);
     var frag = document.createDocumentFragment();
     for (var i = 0; i < coll.length; i++) {
-      var val = isLambda(fn) ? renderLambdaDOM(fn, [coll[i]], env) : renderDOM(fn(coll[i]), env);
+      var val = isLambda(fn) ? renderLambdaDOM(fn, [coll[i]], env, ns) : renderDOM(fn(coll[i]), env, ns);
       frag.appendChild(val);
     }
     return frag;
   };
 
-  RENDER_FORMS["map-indexed"] = function (expr, env) {
+  RENDER_FORMS["map-indexed"] = function (expr, env, ns) {
     var fn = sxEval(expr[1], env), coll = sxEval(expr[2], env);
     var frag = document.createDocumentFragment();
     for (var i = 0; i < coll.length; i++) {
-      var val = isLambda(fn) ? renderLambdaDOM(fn, [i, coll[i]], env) : renderDOM(fn(i, coll[i]), env);
+      var val = isLambda(fn) ? renderLambdaDOM(fn, [i, coll[i]], env, ns) : renderDOM(fn(i, coll[i]), env, ns);
       frag.appendChild(val);
     }
     return frag;
   };
 
-  RENDER_FORMS["filter"] = function (expr, env) {
+  RENDER_FORMS["filter"] = function (expr, env, ns) {
     var result = sxEval(expr, env);
-    return renderDOM(result, env);
+    return renderDOM(result, env, ns);
   };
 
-  RENDER_FORMS["for-each"] = function (expr, env) {
+  RENDER_FORMS["for-each"] = function (expr, env, ns) {
     var fn = sxEval(expr[1], env), coll = sxEval(expr[2], env);
     var frag = document.createDocumentFragment();
     for (var i = 0; i < coll.length; i++) {
-      var val = isLambda(fn) ? renderLambdaDOM(fn, [coll[i]], env) : renderDOM(fn(coll[i]), env);
+      var val = isLambda(fn) ? renderLambdaDOM(fn, [coll[i]], env, ns) : renderDOM(fn(coll[i]), env, ns);
       frag.appendChild(val);
     }
     return frag;
   };
 
-  function renderLambdaDOM(fn, args, env) {
+  function renderLambdaDOM(fn, args, env, ns) {
     var local = merge({}, fn.closure, env);
     for (var i = 0; i < fn.params.length; i++) local[fn.params[i]] = args[i];
-    return renderDOM(fn.body, local);
+    return renderDOM(fn.body, local, ns);
   }
 
   /** True when the array expr is a render-only form (HTML tag, <>, raw!, ~comp). */
@@ -1187,7 +1194,7 @@
     var h = v[0];
     if (!isSym(h)) return false;
     var n = h.name;
-    return !!(HTML_TAGS[n] || SVG_TAGS[n] || n === "<>" || n === "raw!" || n.charAt(0) === "~");
+    return !!(HTML_TAGS[n] || SVG_TAGS[n] || n === "<>" || n === "raw!" || n.charAt(0) === "~" || n.indexOf("html:") === 0 || n.indexOf("-") > 0);
   }
 
   function renderComponentDOM(comp, args, env) {
@@ -1235,7 +1242,7 @@
     return renderDOM(comp.body, local);
   }
 
-  function renderList(expr, env) {
+  function renderList(expr, env, ns) {
     var head = expr[0];
 
     if (isSym(head)) {
@@ -1273,21 +1280,28 @@
       // <> → fragment
       if (name === "<>") {
         var f = document.createDocumentFragment();
-        for (var fi = 1; fi < expr.length; fi++) f.appendChild(renderDOM(expr[fi], env));
+        for (var fi = 1; fi < expr.length; fi++) f.appendChild(renderDOM(expr[fi], env, ns));
         return f;
       }
 
+      // html: prefix → force element rendering
+      if (name.indexOf("html:") === 0) return renderElement(name.substring(5), expr.slice(1), env, ns);
+
       // Render-aware special forms
-      if (RENDER_FORMS[name]) return RENDER_FORMS[name](expr, env);
+      // If name is also an HTML tag and first arg is Keyword → tag call
+      if (RENDER_FORMS[name]) {
+        if (HTML_TAGS[name] && expr.length > 1 && isKw(expr[1])) return renderElement(name, expr.slice(1), env, ns);
+        return RENDER_FORMS[name](expr, env, ns);
+      }
 
       // Macro expansion
       if (name in env && isMacro(env[name])) {
         var mExpanded = expandMacro(env[name], expr.slice(1), env);
-        return renderDOM(mExpanded, env);
+        return renderDOM(mExpanded, env, ns);
       }
 
       // HTML tag
-      if (HTML_TAGS[name]) return renderElement(name, expr.slice(1), env);
+      if (HTML_TAGS[name]) return renderElement(name, expr.slice(1), env, ns);
 
       // Component
       if (name.charAt(0) === "~") {
@@ -1303,23 +1317,34 @@
         return warn;
       }
 
+      // Custom element (hyphenated name) → render as element
+      if (name.indexOf("-") > 0) return renderElement(name, expr.slice(1), env, ns);
+
+      // SVG/MathML namespace auto-detection: inside (svg ...) or (math ...),
+      // unknown tags are created with the inherited namespace
+      if (ns) return renderElement(name, expr.slice(1), env, ns);
+
       // Fallback: evaluate then render
-      return renderDOM(sxEval(expr, env), env);
+      return renderDOM(sxEval(expr, env), env, ns);
     }
 
     // Lambda/list head → evaluate
-    if (isLambda(head) || Array.isArray(head)) return renderDOM(sxEval(expr, env), env);
+    if (isLambda(head) || Array.isArray(head)) return renderDOM(sxEval(expr, env), env, ns);
 
     // Data list
     var dl = document.createDocumentFragment();
-    for (var di = 0; di < expr.length; di++) dl.appendChild(renderDOM(expr[di], env));
+    for (var di = 0; di < expr.length; di++) dl.appendChild(renderDOM(expr[di], env, ns));
     return dl;
   }
 
-  function renderElement(tag, args, env) {
-    var el = SVG_TAGS[tag]
-      ? document.createElementNS(SVG_NS, tag)
-      : document.createElement(tag);
+  function renderElement(tag, args, env, ns) {
+    // Detect namespace from tag: svg → SVG_NS, math → MATH_NS
+    if (tag === "svg") ns = SVG_NS;
+    else if (tag === "math") ns = MATH_NS;
+
+    var el = ns
+      ? document.createElementNS(ns, tag)
+      : (SVG_TAGS[tag] ? document.createElementNS(SVG_NS, tag) : document.createElement(tag));
 
     var extraClass = null;
     var i = 0;
@@ -1345,7 +1370,7 @@
       } else {
         // Child
         if (!(tag in VOID_ELEMENTS)) {
-          el.appendChild(renderDOM(arg, env));
+          el.appendChild(renderDOM(arg, env, ns));
         }
         i++;
       }

shared/sx/async_eval.py

@@ -29,7 +29,7 @@ from .primitives_io import IO_PRIMITIVES, RequestContext, execute_io
 from .parser import SxExpr, serialize
 from .html import (
     HTML_TAGS, VOID_ELEMENTS, BOOLEAN_ATTRS,
-    escape_text, escape_attr, _RawHTML, css_class_collector,
+    escape_text, escape_attr, _RawHTML, css_class_collector, _svg_context,
 )
 
 
@@ -643,9 +643,16 @@ async def _arender_list(expr: list, env: dict[str, Any], ctx: RequestContext) ->
                 parts.append(await _arender(child, env, ctx))
             return "".join(parts)
 
+        # html: prefix → force tag rendering
+        if name.startswith("html:"):
+            return await _arender_element(name[5:], expr[1:], env, ctx)
+
         # Render-aware special forms
+        # If name is also an HTML tag and first arg is Keyword → tag call
         arsf = _ASYNC_RENDER_FORMS.get(name)
         if arsf is not None:
+            if name in HTML_TAGS and len(expr) > 1 and isinstance(expr[1], Keyword):
+                return await _arender_element(name, expr[1:], env, ctx)
             return await arsf(expr, env, ctx)
 
         # Macro expansion
@@ -665,6 +672,14 @@ async def _arender_list(expr: list, env: dict[str, Any], ctx: RequestContext) ->
             if isinstance(val, Component):
                 return await _arender_component(val, expr[1:], env, ctx)
 
+        # Custom element (hyphenated name) → render as tag
+        if "-" in name:
+            return await _arender_element(name, expr[1:], env, ctx)
+
+        # SVG/MathML context → unknown names are child elements
+        if _svg_context.get(False):
+            return await _arender_element(name, expr[1:], env, ctx)
+
         # Fallback — evaluate then render
         result = await async_eval(expr, env, ctx)
         return await _arender(result, env, ctx)
@@ -731,9 +746,19 @@ async def _arender_element(
     if tag in VOID_ELEMENTS:
         return opening
 
-    child_parts = []
-    for child in children:
-        child_parts.append(await _arender(child, env, ctx))
+    # SVG/MathML namespace auto-detection: set context for children
+    token = None
+    if tag in ("svg", "math"):
+        token = _svg_context.set(True)
+
+    try:
+        child_parts = []
+        for child in children:
+            child_parts.append(await _arender(child, env, ctx))
+    finally:
+        if token is not None:
+            _svg_context.reset(token)
+
     return f"{opening}{''.join(child_parts)}</{tag}>"
 
 
@@ -1063,14 +1088,21 @@ async def _aser(expr: Any, env: dict[str, Any], ctx: RequestContext) -> Any:
         if name == "raw!":
             return await _aser_call("raw!", expr[1:], env, ctx)
 
+        # html: prefix → force tag serialization
+        if name.startswith("html:"):
+            return await _aser_call(name[5:], expr[1:], env, ctx)
+
         # Component call — serialize (don't expand)
         if name.startswith("~"):
             return await _aser_call(name, expr[1:], env, ctx)
 
         # Serialize-mode special/HO forms (checked BEFORE HTML_TAGS
-        # because some names like "map" are both HTML tags and sx forms)
+        # because some names like "map" are both HTML tags and sx forms).
+        # If name is also an HTML tag and first arg is Keyword → tag call.
         sf = _ASER_FORMS.get(name)
         if sf is not None:
+            if name in HTML_TAGS and len(expr) > 1 and isinstance(expr[1], Keyword):
+                return await _aser_call(name, expr[1:], env, ctx)
             return await sf(expr, env, ctx)
 
         # HTML tag — serialize (don't render to HTML)
@@ -1084,6 +1116,14 @@ async def _aser(expr: Any, env: dict[str, Any], ctx: RequestContext) -> Any:
                 expanded = _expand_macro(val, expr[1:], env)
                 return await _aser(expanded, env, ctx)
 
+        # Custom element (hyphenated name) → serialize as tag
+        if "-" in name:
+            return await _aser_call(name, expr[1:], env, ctx)
+
+        # SVG/MathML context → unknown names are child elements
+        if _svg_context.get(False):
+            return await _aser_call(name, expr[1:], env, ctx)
+
     # Function / lambda call — evaluate (produces data, not rendering)
     fn = await async_eval(head, env, ctx)
     args = [await async_eval(a, env, ctx) for a in expr[1:]]
@@ -1150,32 +1190,41 @@ async def _aser_call(
 ) -> SxExpr:
     """Serialize ``(name :key val child ...)`` — evaluate args but keep
     as sx source instead of rendering to HTML."""
-    parts = [name]
-    extra_class: str | None = None  # from :style StyleValue conversion
-    i = 0
-    while i < len(args):
-        arg = args[i]
-        if isinstance(arg, Keyword) and i + 1 < len(args):
-            val = await _aser(args[i + 1], env, ctx)
-            if val is not NIL and val is not None:
-                # :style StyleValue → convert to :class and register CSS
-                if arg.name == "style" and isinstance(val, StyleValue):
-                    from .css_registry import register_generated_rule
-                    register_generated_rule(val)
-                    extra_class = val.class_name
-                else:
-                    parts.append(f":{arg.name}")
-                    parts.append(serialize(val))
-            i += 2
-        else:
-            result = await _aser(arg, env, ctx)
-            if result is not NIL and result is not None:
-                parts.append(serialize(result))
-            i += 1
-    # If we converted a :style to a class, merge into existing :class or add it
-    if extra_class:
-        _merge_class_into_parts(parts, extra_class)
-    return SxExpr("(" + " ".join(parts) + ")")
+    # SVG/MathML namespace auto-detection for serializer
+    token = None
+    if name in ("svg", "math"):
+        token = _svg_context.set(True)
+
+    try:
+        parts = [name]
+        extra_class: str | None = None  # from :style StyleValue conversion
+        i = 0
+        while i < len(args):
+            arg = args[i]
+            if isinstance(arg, Keyword) and i + 1 < len(args):
+                val = await _aser(args[i + 1], env, ctx)
+                if val is not NIL and val is not None:
+                    # :style StyleValue → convert to :class and register CSS
+                    if arg.name == "style" and isinstance(val, StyleValue):
+                        from .css_registry import register_generated_rule
+                        register_generated_rule(val)
+                        extra_class = val.class_name
+                    else:
+                        parts.append(f":{arg.name}")
+                        parts.append(serialize(val))
+                i += 2
+            else:
+                result = await _aser(arg, env, ctx)
+                if result is not NIL and result is not None:
+                    parts.append(serialize(result))
+                i += 1
+        # If we converted a :style to a class, merge into existing :class or add it
+        if extra_class:
+            _merge_class_into_parts(parts, extra_class)
+        return SxExpr("(" + " ".join(parts) + ")")
+    finally:
+        if token is not None:
+            _svg_context.reset(token)
 
 
 def _merge_class_into_parts(parts: list[str], class_name: str) -> None:

shared/sx/html.py

@@ -44,6 +44,12 @@ css_class_collector: contextvars.ContextVar[set[str] | None] = contextvars.Conte
     "css_class_collector", default=None
 )
 
+# ContextVar for SVG/MathML namespace auto-detection.
+# When True, unknown tag names inside (svg ...) or (math ...) are treated as elements.
+_svg_context: contextvars.ContextVar[bool] = contextvars.ContextVar(
+    "_svg_context", default=False
+)
+
 
 class _RawHTML:
     """Marker for pre-rendered HTML that should not be escaped."""
@@ -430,10 +436,19 @@ def _render_list(expr: list, env: dict[str, Any]) -> str:
         if name == "<>":
             return "".join(_render(child, env) for child in expr[1:])
 
+        # --- html: prefix → force tag rendering --------------------------
+        if name.startswith("html:"):
+            return _render_element(name[5:], expr[1:], env)
+
         # --- Render-aware special forms --------------------------------------
         # Check BEFORE HTML_TAGS because some names overlap (e.g. `map`).
-        if name in _RENDER_FORMS:
-            return _RENDER_FORMS[name](expr, env)
+        # But if the name is ALSO an HTML tag and first arg is a Keyword,
+        # it's a tag call (e.g. (filter :id "x" ...)), not a HO function.
+        rsf = _RENDER_FORMS.get(name)
+        if rsf is not None:
+            if name in HTML_TAGS and len(expr) > 1 and isinstance(expr[1], Keyword):
+                return _render_element(name, expr[1:], env)
+            return rsf(expr, env)
 
         # --- Macro expansion → expand then render --------------------------
         if name in env:
@@ -453,6 +468,14 @@ def _render_list(expr: list, env: dict[str, Any]) -> str:
                 return _render_component(val, expr[1:], env)
             # Fall through to evaluation
 
+        # --- Custom element (hyphenated name) → render as tag ------------
+        if "-" in name:
+            return _render_element(name, expr[1:], env)
+
+        # --- SVG/MathML context → unknown names are child elements --------
+        if _svg_context.get(False):
+            return _render_element(name, expr[1:], env)
+
         # --- Other special forms / function calls → evaluate then render ---
         result = _eval(expr, env)
         return _render(result, env)
@@ -524,7 +547,15 @@ def _render_element(tag: str, args: list, env: dict[str, Any]) -> str:
     if tag in VOID_ELEMENTS:
         return opening
 
-    # Render children
-    child_html = "".join(_render(child, env) for child in children)
+    # SVG/MathML namespace auto-detection: set context for children
+    token = None
+    if tag in ("svg", "math"):
+        token = _svg_context.set(True)
+
+    try:
+        child_html = "".join(_render(child, env) for child in children)
+    finally:
+        if token is not None:
+            _svg_context.reset(token)
 
     return f"{opening}{child_html}</{tag}>"