Blogger XML Attributes: Practical Guide

If you build or customize Blogger themes, you’ve probably bumped into mysterious attributes on the opening <html> tag: things like b:layoutsVersion, b:defaultwidgetversion, b:render, b:css, b:js, and the familiar XML namespaces for b, data, and expr. They look small, but they control big pieces of how your template renders—what layout engine is used, which gadget model is active, whether Blogger injects stock CSS/JS, and how expressions are parsed.

This guide translates those switches into plain English. We’ll walk through what each attribute does, when to use it, and the gotchas that tend to trip people up. You’ll get copy-ready code, a step-by-step setup, deeper explanations, advanced tricks, FAQs, and a quick troubleshooting section—so you can ship clean, fast, and predictable Blogger themes.

Introduction: HTML, XML, and Blogger’s Template Engine

At its core, a Blogger theme is HTML with XML-flavored templating. The browser sees normal HTML, but before that, Blogger’s server parses the template: resolving data tags, evaluating expr: expressions, and applying layout logic. That’s why the root <html> element often carries XML namespaces and b:* attributes—these tell the template engine how to interpret and assemble your final page.

You’ll also see references to <?xml ... ?> and <!DOCTYPE html>. The doctype declares modern HTML5 to the browser. The optional XML prolog is not required for Blogger themes and can be omitted; what matters most are the namespaces and b:* attributes on <html>.

Step-by-Step: Set the Right XML & Blogger Attributes

Start with a valid HTML5 shell.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Document</title>
  </head>
  <body>

This is the browser’s baseline. We’ll add Blogger specifics next.

Add required XML namespaces.

<html
  xmlns='http://www.w3.org/1999/xhtml'
  xmlns:b='http://www.google.com/2005/gml/b'
  xmlns:data='http://www.google.com/2005/gml/data'
  xmlns:expr='http://www.google.com/2005/gml/expr'
  lang="en">

These namespaces activate Blogger’s template grammar: <b:...> widgets, <data:...> bindings, and expr: attributes.

Choose your layout version.
Blogger supports multiple layout engines. If you don’t set one, you’re effectively on version 1.
- Layout v1: <html>
- Layout v2: <html b:version='2'>
- Layout v3 (current standard): <html b:layoutsVersion='3'>
Version 3 unlocks the modern layout manager, richer widget controls, and generally the best editing experience. It’s what most new themes target.
Match the gadget (widget) version to your layout.
Gadgets have versions too, and they map to your chosen layout:
- Layout 1 → Gadget 1: no need to declare anything.
- Layout 2 → Gadget 1: still default.
- Layout 3 → Gadget 2: declare b:defaultwidgetversion='2'.
```
<html
  b:layoutsVersion='3'
  b:defaultwidgetversion='2'
  xmlns='http://www.w3.org/1999/xhtml'
  xmlns:b='http://www.google.com/2005/gml/b'
  xmlns:data='http://www.google.com/2005/gml/data'
  xmlns:expr='http://www.google.com/2005/gml/expr'
  lang="en">
```
Using the wrong pair can break widget editing or render unexpected markup.
Control Blogger’s auto CSS and JS.
Blogger injects platform CSS and JS by default. You can opt out if you’re shipping a fully custom stack.
- b:css='true|false' — include or disable Blogger’s CSS bundles.
- b:js='true|false' — include or disable Blogger’s JS bundles.
```
<html
  b:layoutsVersion='3'
  b:defaultwidgetversion='2'
  b:css='false'
  b:js='true'
  ...>
```
Common pattern: keep JS (widget logic, editor support) but disable CSS to avoid style conflicts.
Decide whether Blogger should render widgets/HTML.
b:render='true|false' controls whether the platform renders widgets. Leave it true unless you’re building a special shell.
```
<html b:render='true' ...>
```
Add optional template metadata.
These aren’t required but help with maintenance:
- b:responsive='true|false' — documents that your template is responsive.
- b:templateUrl='koderian.xml' — a human-readable name or source reference.
- b:templateVersion='1.0.0' — semantic versioning for your theme.
```
<html
  b:layoutsVersion='3'
  b:defaultwidgetversion='2'
  b:responsive='true'
  b:templateUrl='koderian.xml'
  b:templateVersion='1.0.0'
  ...>
```

Deeper Explanation: What Each Attribute Really Does

`b:layoutsVersion` vs `b:version`

Both relate to the layout engine, but b:layoutsVersion='3' is the modern, preferred flag. Version 3 unlocks the current gadget architecture and layout editor. Older themes may use b:version='2', which is fine but more limited. If you’re starting fresh, pick version 3 and stick with it.

`b:defaultwidgetversion`

This sets the gadget model used when rendering widgets. Version 2 pairs with layout v3 and exposes newer widget features. If you forget to declare it on a v3 layout, some gadgets might fall back or behave inconsistently in the designer.

`b:render`

Think of this as a master switch for platform rendering. With true (default), Blogger processes your widgets and data bindings. With false, it won’t—useful only for highly custom shells (rare). For almost every theme, leave it on.

`b:css` and `b:js`

These toggle Blogger’s built-in CSS and JS includes. Turning CSS off avoids clashes if your design system already resets and styles every widget. Turning JS off removes Blogger’s widget logic and can break the editor experience—only do it if you fully understand the trade-offs.

XML Namespaces (`xmlns`)

The namespaces declare where each special tag/attribute “lives” so the template processor can understand them:

xmlns — base XHTML namespace
xmlns:b — Blogger widget elements (<b:section>, <b:widget>, etc.)
xmlns:data — data bindings (<data:post.title/>)
xmlns:expr — expression attributes (expr:src, expr:class)

Do not omit these; without them, Blogger-specific tags/attributes won’t parse correctly.

Copy-Ready Templates (Minimal → Advanced)

Minimal, Modern Blogger Shell (Recommended)

<!DOCTYPE html>
<html
  lang="en"
  xmlns="http://www.w3.org/1999/xhtml"
  xmlns:b="http://www.google.com/2005/gml/b"
  xmlns:data="http://www.google.com/2005/gml/data"
  xmlns:expr="http://www.google.com/2005/gml/expr"
  b:layoutsVersion="3"
  b:defaultwidgetversion="2"
  b:responsive="true"
  b:templateVersion="1.0.0">




<data:blog.pageTitle/>

Custom Styles, Keep Blogger JS

<html
  ...
  b:css="false"
  b:js="true"
  ...>

Ship your own CSS (Tailwind/vanilla) while preserving editor and widget behavior.

Hard Sandbox (Advanced; Not Typical)

<html
  ...
  b:css="false"
  b:js="false"
  b:render="true"
  ...>

Only use this if you fully replace platform behavior with custom scripts—expect gadgets to lose default interactivity.

Extra Tips & Advanced Use Cases

Version pinning for collaborations: Set b:templateVersion (e.g., 1.2.3) and update it with real releases. It’s a simple way to track client sites running older builds.
CSS conflicts: If you see odd spacing or duplicated styles, disable Blogger CSS (b:css='false') and normalize your own typography, forms, and widget lists.
Performance first: If you keep Blogger JS, lazy-load heavy widgets inside the template using intersection observers or <b:if cond='...'> guards to minimize DOM bloat on first paint.
Safer refactors: When changing layout/gadget versions, clone the theme first. Some older widgets serialize settings differently across versions.
Accessibility: Layout v3 + proper expr: lets you auto-generate alt, aria-label, and IDs programmatically. Bake this in early.

FAQ

Do I need the `<?xml ... ?>` prolog?

No. Blogger themes render fine without it. The key parts are the HTML5 doctype, namespaces, and your b:* attributes.

Which layout version should I use today?

Use layout v3 (b:layoutsVersion='3') with gadget v2 (b:defaultwidgetversion='2'). It’s the most capable and best supported.

Is it safe to disable Blogger CSS?

Yes—if your template includes a complete style system and you’re prepared to style all widgets. Otherwise, keep it enabled to avoid unstyled components.

What breaks if I set `b:js='false'`?

Platform scripts that power widgets, editor features, or dynamic behaviors may not run. Only disable JS if you know exactly what you’re replacing.

Why are my Blogger tags not recognized?

Missing namespaces. Make sure the xmlns attributes for b, data, and expr are present on the <html> element.

Troubleshooting

Widgets not editable in Layout: Confirm b:layoutsVersion='3' and b:defaultwidgetversion='2'. If you migrated from v1/v2, recreate misbehaving widgets.
Styles look doubled or off: You might be loading both Blogger CSS and your own framework. Set b:css='false' and rebuild your component styles.
Script errors after disabling JS: Re-enable b:js='true' and remove duplicate libraries. Then progressively opt out of what you truly replace.
Data tags render verbatim: Namespaces missing or malformed. Re-check the xmlns lines; typos break parsing.
Layout editor options missing: You may not actually be on layout v3. Inspect the rendered HTML; if b:layoutsVersion is absent, you’re on v1.

Worked Examples You Can Paste

1) Production-Ready HTML Tag

<html
  lang="en"
  xmlns="http://www.w3.org/1999/xhtml"
  xmlns:b="http://www.google.com/2005/gml/b"
  xmlns:data="http://www.google.com/2005/gml/data"
  xmlns:expr="http://www.google.com/2005/gml/expr"
  b:layoutsVersion="3"
  b:defaultwidgetversion="2"
  b:css="false"
  b:js="true"
  b:responsive="true"
  b:templateUrl="koderian.xml"
  b:templateVersion="1.3.0">

2) Safe Fallback to Platform CSS, Custom JS Only

<html
  ...
  b:css="true"
  b:js="false"
  ...>

Use this if you prefer Blogger’s default styling but want zero platform JS (rare). Test widgets thoroughly.

3) Debug Mode: Verify Namespaces & Versions

<!-- Inspect these in your rendered HTML source -->
<html
  xmlns="http://www.w3.org/1999/xhtml"
  xmlns:b="http://www.google.com/2005/gml/b"
  xmlns:data="http://www.google.com/2005/gml/data"
  xmlns:expr="http://www.google.com/2005/gml/expr"
  b:layoutsVersion="3"
  b:defaultwidgetversion="2" ...>

Putting It All Together

Here’s a compact template skeleton that shows the typical, modern configuration—layout v3, gadget v2, platform JS on, platform CSS off, and fully declared namespaces:

<!DOCTYPE html>
<html
  lang="en"
  xmlns="http://www.w3.org/1999/xhtml"
  xmlns:b="http://www.google.com/2005/gml/b"
  xmlns:data="http://www.google.com/2005/gml/data"
  xmlns:expr="http://www.google.com/2005/gml/expr"
  b:layoutsVersion="3"
  b:defaultwidgetversion="2"
  b:css="false"
  b:js="true"
  b:responsive="true"
  b:templateUrl="koderian.xml"
  b:templateVersion="1.0.0">

  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title><data:blog.pageTitle /></title>
    <!-- Your CSS here -->
  </head>

  <body>
    <b:section id='header' maxwidgets='2' showaddelement='yes'>
      <b:widget id='Header1' type='Header' />
    </b:section>

    <b:section id='main' showaddelement='yes'>
      <b:widget id='Blog1' type='Blog' />
    </b:section>

    <b:section id='footer' showaddelement='yes'>
      <b:widget id='Text1' type='Text' />
    </b:section>

    <!-- Your JS here -->
  </body>

</html>

Conclusion

Those tiny attributes on the <html> tag control the shape of your entire Blogger theme. Choose the modern layout engine (b:layoutsVersion='3'), pair it with the right gadget version (b:defaultwidgetversion='2'), and then decide how much of Blogger’s default CSS/JS you want. Keep the XML namespaces intact, and document your template with b:responsive, b:templateUrl, and b:templateVersion so future updates are painless.

If this guide helped, bookmark it for later, share it with a fellow Blogger developer, and subscribe to catch upcoming deep dives on expressions, widgets, and performance tuning.

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