@data-passthrough : The Style Passthrough Attribute

The data-passthrough attribute controls style inheritance for embedded content in <iframe> elements. It determines whether styles from the parent document should be applied to externally loaded content, enabling both style isolation and consistent theming across document composition.

Summary

The data-passthrough attribute manages style inheritance for iframe content:

Controls whether parent document styles affect embedded content
Defaults to false (style isolation)
When true, enables style passthrough for consistent theming
Only applies to <iframe> elements, not <embed>
Critical for modular document composition with unified styling
Enables both isolated and themed content inclusion scenarios

This attribute is essential for:

Creating themed multi-section documents
Maintaining consistent typography across embedded content
Isolating external content styles when needed
Building reusable templates with or without parent styling
Controlling visual consistency in document assembly
Managing style inheritance in complex document structures

Usage

The data-passthrough attribute is used exclusively with <iframe> elements:

<!-- Default: style isolation (passthrough=false) -->
<iframe src="external-content.html"></iframe>

<!-- Explicit isolation -->
<iframe src="external-content.html" data-passthrough="false"></iframe>

<!-- Enable style passthrough -->
<iframe src="external-content.html" data-passthrough="true"></iframe>

<!-- With data binding -->
<iframe src=""
        data-passthrough=""></iframe>

Supported Elements

The data-passthrough attribute is supported exclusively on:

Iframe Element

<iframe> - The inline frame element for embedded content

Not supported on:

<embed> - Embed always inherits parent styles
<object> - Object is for file attachments, not parsed content
Other elements - Attribute is specific to iframe style management

Binding Values

Boolean Values

Type: boolean Default: false Binding: Supports data binding expressions

<!-- Static values -->
<iframe src="content.html" data-passthrough="true"></iframe>
<iframe src="content.html" data-passthrough="false"></iframe>

<!-- Data binding -->
<iframe src=""
        data-passthrough=""></iframe>

<!-- Conditional passthrough -->
<iframe src=""
        data-passthrough=""></iframe>

<!-- Expression -->
<iframe src="content.html"
        data-passthrough=""></iframe>

Data Model Example:

public class DocumentModel
{
    public string TemplateUrl { get; set; }
    public bool ApplyTheme { get; set; }
    public string SectionType { get; set; }
    public bool UseCustomTheme { get; set; }
}

Notes

How Style Passthrough Works

The data-passthrough attribute fundamentally changes how styles are applied to iframe content:

passthrough=”false” (default):

<style>
    body {
        font-family: Arial;
        color: #333;
        font-size: 12pt;
    }
</style>

<iframe src="section.html" data-passthrough="false">
    <!-- Embedded content uses ONLY its own styles -->
    <!-- Parent body styles are NOT applied -->
    <!-- Content renders with its own defined styles -->
</iframe>

passthrough=”true”:

<style>
    body {
        font-family: Arial;
        color: #333;
        font-size: 12pt;
    }
</style>

<iframe src="section.html" data-passthrough="true">
    <!-- Embedded content INHERITS parent styles -->
    <!-- Parent body styles ARE applied -->
    <!-- Content uses parent typography, colors, etc. -->
</iframe>

Style Isolation (passthrough=false)

When style passthrough is disabled (default behavior):

Isolated Rendering: Embedded content uses only its own defined styles
No Inheritance: Parent document styles do not affect embedded content
Independent Theming: Each embedded document controls its own appearance
Clean Separation: Useful for including third-party content
Predictable Output: Embedded content looks exactly as designed

Use cases:

Including content with its own complete styling
Embedding third-party templates
Maintaining style independence between sections
Loading content that should not be themed
Testing embedded content in isolation

<!-- Each section maintains its own styles -->
<iframe src="marketing-section.html" data-passthrough="false"></iframe>
<iframe src="technical-section.html" data-passthrough="false"></iframe>
<iframe src="legal-section.html" data-passthrough="false"></iframe>

Style Passthrough (passthrough=true)

When style passthrough is enabled:

Style Inheritance: Embedded content inherits parent styles
Unified Theming: Consistent look across all sections
Typography Consistency: Fonts, sizes, and colors match parent
Theme Application: Brand colors and styles flow through
Reduced Duplication: No need to repeat styles in each section

Use cases:

Creating themed multi-section documents
Maintaining brand consistency
Building document assembly systems
Applying corporate style guides
Creating unified reports from multiple sources

<!-- All sections inherit parent theme -->
<style>
    body {
        font-family: 'Corporate Sans', Arial, sans-serif;
        color: #2c3e50;
        font-size: 11pt;
        line-height: 1.6;
    }
    h1 { color: #336699; font-size: 18pt; }
    h2 { color: #5588bb; font-size: 14pt; }
</style>

<iframe src="section1.html" data-passthrough="true"></iframe>
<iframe src="section2.html" data-passthrough="true"></iframe>
<iframe src="section3.html" data-passthrough="true"></iframe>

iframe vs embed Behavior

Key difference in style handling:

iframe with data-passthrough:

Extends Div component
Supports data-passthrough attribute
Default: Style isolation (passthrough=false)
Controllable style inheritance
Best for complex content with style control needs

embed element:

Extends VisualComponent directly
Does not support data-passthrough
Always inherits parent styles
No style isolation capability
Best for simple content fragments that should match parent theme

<!-- iframe: controlled style inheritance -->
<iframe src="content.html" data-passthrough="false">
    <!-- Isolated styles -->
</iframe>

<!-- embed: always inherits parent styles -->
<embed src="content.html" />
<!-- Always styled like parent -->

Which Styles Pass Through?

When data-passthrough="true", these styles are inherited:

Typography:

font-family, font-size, font-weight, font-style
line-height, letter-spacing, word-spacing
text-decoration, text-transform

Colors:

color (text color)
background-color

Text Layout:

text-align, text-indent
white-space, word-break

Spacing (from parent container):

Inherited spacing properties

Embedded content can still override:

<!-- Parent document -->
<style>
    body { font-family: Arial; color: #333; }
</style>

<iframe src="section.html" data-passthrough="true"></iframe>

<!-- section.html can override -->
<style>
    h1 { color: #ff0000; }  /* Overrides parent color for h1 */
</style>

Default Behavior

If data-passthrough is not specified:

<!-- These are equivalent -->
<iframe src="content.html"></iframe>
<iframe src="content.html" data-passthrough="false"></iframe>

The default is style isolation (passthrough=false) to maintain backward compatibility and prevent unexpected style bleeding.

Performance Implications

Style passthrough has minimal performance impact:

passthrough=false: Returns empty style object, fastest
passthrough=true: Applies parent styles, minimal overhead
No significant difference for typical documents
Consider style complexity, not passthrough setting

Document Assembly Patterns

Common patterns for document composition:

Pattern 1: Fully Themed Document

<!-- All sections inherit company theme -->
<style>
    @import url('company-theme.css');
</style>

<iframe src="sections/intro.html" data-passthrough="true"></iframe>
<iframe src="sections/analysis.html" data-passthrough="true"></iframe>
<iframe src="sections/conclusion.html" data-passthrough="true"></iframe>

Pattern 2: Mixed Theming

<!-- Some themed, some isolated -->
<iframe src="branded-header.html" data-passthrough="true"></iframe>
<iframe src="third-party-content.html" data-passthrough="false"></iframe>
<iframe src="branded-footer.html" data-passthrough="true"></iframe>

Pattern 3: Conditional Theming

<!-- Theme based on document type -->
<iframe src=".html"
        data-passthrough=""></iframe>

Debugging Style Issues

To diagnose style inheritance problems:

Check passthrough setting: Verify true/false value
Inspect embedded content: Look at content’s own styles
Review parent styles: Ensure parent has styles to inherit
Test isolation: Try both true and false to see difference
Use fallback: Include complete styles in embedded content

<!-- Debug: explicitly show both versions -->
<h2>With Passthrough (inherits parent)</h2>
<iframe src="test.html" data-passthrough="true"></iframe>

<h2>Without Passthrough (isolated)</h2>
<iframe src="test.html" data-passthrough="false"></iframe>

Best Practices

When to use passthrough=true:

Building themed document assemblies
Maintaining brand consistency
Applying corporate style guides
Creating unified multi-section reports
Developing reusable template libraries

When to use passthrough=false:

Including third-party content
Embedding content with complete styling
Maintaining style independence
Testing embedded content in isolation
Preventing style conflicts

General guidance:

Be consistent within a document
Document your choice in comments
Test both isolated and themed views
Provide complete fallback styles in embedded content
Use conditional passthrough for flexible systems

Examples

1. Basic Style Isolation (Default)

Embedded content maintains its own styles:

<!-- main.html -->
<!DOCTYPE html>
<html>
<head>
    <style>
        body {
            font-family: 'Georgia', serif;
            color: #000;
            font-size: 14pt;
        }
    </style>
</head>
<body>
    <h1>Main Document</h1>

    <!-- Embedded content uses its own styles -->
    <iframe src="section.html"></iframe>
</body>
</html>

<!-- section.html -->
<style>
    /* These styles apply, parent styles don't -->
    body {
        font-family: 'Arial', sans-serif;
        color: #333;
        font-size: 11pt;
    }
</style>

<h2>Section Content</h2>
<p>This uses Arial 11pt, not Georgia 14pt.</p>

2. Enable Style Passthrough for Theming

All sections inherit parent theme:

<!-- main.html -->
<!DOCTYPE html>
<html>
<head>
    <style>
        body {
            font-family: 'Helvetica Neue', sans-serif;
            color: #2c3e50;
            font-size: 11pt;
            line-height: 1.6;
        }

        h1 {
            color: #336699;
            font-size: 18pt;
            margin-bottom: 15pt;
        }

        h2 {
            color: #5588bb;
            font-size: 14pt;
            margin-top: 20pt;
        }
    </style>
</head>
<body>
    <h1>Annual Report 2024</h1>

    <!-- All sections inherit parent styles -->
    <iframe src="sections/executive-summary.html" data-passthrough="true"></iframe>
    <iframe src="sections/financial-overview.html" data-passthrough="true"></iframe>
    <iframe src="sections/future-outlook.html" data-passthrough="true"></iframe>
</body>
</html>

3. Conditional Style Passthrough

Apply theme based on content type:

<!-- Model: { sections: [{url: "a.html", themed: true}, {url: "b.html", themed: false}] } -->

<style>
    body {
        font-family: 'Open Sans', sans-serif;
        color: #333;
    }
</style>

<template data-bind="">
    <iframe src=""
            data-passthrough=""
            style="margin-bottom: 20pt;"></iframe>
</template>

4. Corporate Theme Application

Apply corporate branding to all sections:

<!DOCTYPE html>
<html>
<head>
    <title>Corporate Document</title>
    <style>
        /* Corporate theme */
        @import url('https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap');

        body {
            font-family: 'Roboto', Arial, sans-serif;
            color: #1a1a1a;
            font-size: 10pt;
            line-height: 1.5;
        }

        h1, h2, h3 {
            color: #0066cc;
            font-weight: 700;
        }

        h1 { font-size: 20pt; }
        h2 { font-size: 16pt; }
        h3 { font-size: 13pt; }

        a {
            color: #0066cc;
            text-decoration: none;
        }

        .highlight {
            background-color: #ffeb3b;
            padding: 2pt 4pt;
        }
    </style>
</head>
<body>
    <div style="text-align: center; margin-bottom: 40pt;">
        <h1>Acme Corporation</h1>
        <p>Quarterly Business Review</p>
    </div>

    <!-- All sections use corporate theme -->
    <iframe src="sections/overview.html" data-passthrough="true"></iframe>
    <iframe src="sections/metrics.html" data-passthrough="true"></iframe>
    <iframe src="sections/goals.html" data-passthrough="true"></iframe>
</body>
</html>

5. Mixed Themed and Isolated Content

Some sections themed, others isolated:

<!DOCTYPE html>
<html>
<head>
    <style>
        body {
            font-family: 'Arial', sans-serif;
            color: #333;
            font-size: 11pt;
        }

        h1 { color: #336699; }
    </style>
</head>
<body>
    <h1>Project Report</h1>

    <!-- Company header: uses theme -->
    <iframe src="templates/company-header.html"
            data-passthrough="true"></iframe>

    <!-- Main content: uses theme -->
    <iframe src="sections/project-overview.html"
            data-passthrough="true"></iframe>

    <!-- External vendor report: isolated -->
    <iframe src="vendor-reports/technical-audit.html"
            data-passthrough="false"></iframe>

    <!-- Company footer: uses theme -->
    <iframe src="templates/company-footer.html"
            data-passthrough="true"></iframe>
</body>
</html>

6. Data-Driven Theme Control

Control theming per section via data:

public class DocumentSection
{
    public string Title { get; set; }
    public string Url { get; set; }
    public bool ApplyBranding { get; set; }
    public string Type { get; set; }
}

public class ReportModel
{
    public List<DocumentSection> Sections { get; set; } = new List<DocumentSection>
    {
        new DocumentSection
        {
            Title = "Cover Page",
            Url = "cover.html",
            ApplyBranding = true,
            Type = "branded"
        },
        new DocumentSection
        {
            Title = "Third-Party Analysis",
            Url = "external-analysis.html",
            ApplyBranding = false,
            Type = "external"
        },
        new DocumentSection
        {
            Title = "Conclusion",
            Url = "conclusion.html",
            ApplyBranding = true,
            Type = "branded"
        }
    };
}

<style>
    body {
        font-family: 'Helvetica', sans-serif;
        color: #2c3e50;
    }
</style>

<h1>Multi-Source Report</h1>

<template data-bind="">
    <div style="page-break-after: always;">
        <h2></h2>
        <iframe src=""
                data-passthrough=""
                title=""></iframe>
    </div>
</template>

Newsletter with consistent article styling:

<!DOCTYPE html>
<html>
<head>
    <title>Monthly Newsletter</title>
    <style>
        body {
            font-family: 'Georgia', serif;
            color: #333;
            font-size: 11pt;
            line-height: 1.8;
        }

        h2 {
            color: #c0392b;
            font-size: 16pt;
            border-bottom: 2pt solid #c0392b;
            padding-bottom: 5pt;
            margin-top: 30pt;
        }

        .article-meta {
            color: #7f8c8d;
            font-size: 9pt;
            font-style: italic;
        }
    </style>
</head>
<body>
    <h1 style="text-align: center; color: #c0392b;">Tech Monthly Newsletter</h1>
    <p style="text-align: center; color: #7f8c8d;">January 2024 Edition</p>

    <!-- All articles inherit newsletter theme -->
    <iframe src="articles/feature-story.html" data-passthrough="true"></iframe>
    <iframe src="articles/tech-review.html" data-passthrough="true"></iframe>
    <iframe src="articles/industry-news.html" data-passthrough="true"></iframe>
    <iframe src="articles/upcoming-events.html" data-passthrough="true"></iframe>
</body>
</html>

8. Dynamic Theme Switching

Switch themes based on user preference:

public class DocumentSettings
{
    public string ThemeMode { get; set; } // "light" or "dark"
    public bool ApplyTheme => ThemeMode == "light" || ThemeMode == "dark";
}

<!-- Model: { settings: { themeMode: "light" } } -->

<style>
    /* Theme based on mode */
    body {
        font-family: 'Segoe UI', sans-serif;
        background-color: ;
        color: ;
        font-size: 11pt;
    }

    h1, h2, h3 {
        color: ;
    }
</style>

<h1>Themed Document</h1>

<!-- Apply theme to all sections -->
<iframe src="section1.html" data-passthrough=""></iframe>
<iframe src="section2.html" data-passthrough=""></iframe>
<iframe src="section3.html" data-passthrough=""></iframe>

9. Multi-Language Document with Consistent Typography

Different languages, same typography:

<!DOCTYPE html>
<html>
<head>
    <style>
        body {
            font-family: 'Noto Sans', Arial, sans-serif;
            color: #2c3e50;
            font-size: 11pt;
            line-height: 1.7;
        }

        h1 {
            font-size: 18pt;
            color: #16a085;
            margin-bottom: 15pt;
        }

        h2 {
            font-size: 14pt;
            color: #27ae60;
            margin-top: 20pt;
        }
    </style>
</head>
<body>
    <!-- Model: { language: "en" } -->

    <h1>Multilingual Report</h1>

    <!-- All language sections use same typography -->
    <iframe src="content//summary.html"
            data-passthrough="true"></iframe>
    <iframe src="content//details.html"
            data-passthrough="true"></iframe>
    <iframe src="content//conclusion.html"
            data-passthrough="true"></iframe>
</body>
</html>

10. Template Library with Style Control

Reusable templates with configurable theming:

public class TemplateSection
{
    public string TemplateName { get; set; }
    public string Path { get; set; }
    public bool UseParentStyles { get; set; }
}

public class TemplateLibraryModel
{
    public string ThemeName { get; set; }
    public List<TemplateSection> Sections { get; set; }
}

<!-- Load theme CSS -->
<link rel="stylesheet" href="themes/.css" />

<h1>Document Assembly</h1>

<template data-bind="">
    <div class="section">
        <h2></h2>
        <iframe src="templates/"
                data-passthrough=""
                title=""></iframe>
    </div>
</template>

11. White-Label Document Generation

Generate documents with different branding:

public class BrandingConfig
{
    public string ClientName { get; set; }
    public string PrimaryColor { get; set; }
    public string SecondaryColor { get; set; }
    public string FontFamily { get; set; }
    public bool ApplyBranding { get; set; }
}

<!-- Model: { branding: {clientName: "Acme", primaryColor: "#0066cc", ...} } -->

<style>
    body {
        font-family: , sans-serif;
        color: #333;
        font-size: 11pt;
    }

    h1, h2, h3 {
        color: ;
    }

    .highlight {
        background-color: ;
        opacity: 0.2;
        padding: 5pt;
    }
</style>

<div style="text-align: center; margin-bottom: 40pt;">
    <h1> Report</h1>
</div>

<!-- Apply client branding to all sections -->
<iframe src="sections/overview.html"
        data-passthrough=""></iframe>
<iframe src="sections/analysis.html"
        data-passthrough=""></iframe>
<iframe src="sections/recommendations.html"
        data-passthrough=""></iframe>

12. Academic Paper with Consistent Formatting

Research paper with uniform citation styles:

<!DOCTYPE html>
<html>
<head>
    <title>Research Paper</title>
    <style>
        body {
            font-family: 'Times New Roman', serif;
            color: #000;
            font-size: 12pt;
            line-height: 2.0;
            text-align: justify;
        }

        h1 {
            font-size: 16pt;
            text-align: center;
            font-weight: bold;
            margin-top: 0;
        }

        h2 {
            font-size: 14pt;
            font-weight: bold;
            margin-top: 24pt;
            margin-bottom: 12pt;
        }

        .citation {
            font-size: 10pt;
            margin-left: 40pt;
        }

        sup {
            font-size: 9pt;
        }
    </style>
</head>
<body>
    <h1>Impact of Technology on Modern Society</h1>
    <p style="text-align: center;">Jane Doe, Ph.D.</p>

    <!-- All sections maintain academic formatting -->
    <iframe src="sections/abstract.html" data-passthrough="true"></iframe>
    <iframe src="sections/introduction.html" data-passthrough="true"></iframe>
    <iframe src="sections/methodology.html" data-passthrough="true"></iframe>
    <iframe src="sections/results.html" data-passthrough="true"></iframe>
    <iframe src="sections/discussion.html" data-passthrough="true"></iframe>
    <iframe src="sections/conclusion.html" data-passthrough="true"></iframe>
    <iframe src="sections/references.html" data-passthrough="true"></iframe>
</body>
</html>

13. Magazine Layout with Section Independence

Magazine with varied section styles:

<!DOCTYPE html>
<html>
<head>
    <title>Design Magazine</title>
    <style>
        body {
            font-family: 'Futura', 'Century Gothic', sans-serif;
            color: #333;
            font-size: 11pt;
        }

        .magazine-header {
            font-size: 32pt;
            font-weight: bold;
            color: #ff6b6b;
            text-align: center;
            margin-bottom: 40pt;
        }
    </style>
</head>
<body>
    <div class="magazine-header">DESIGN WEEKLY</div>

    <!-- Cover story: uses magazine theme -->
    <iframe src="articles/cover-story.html" data-passthrough="true"></iframe>

    <!-- Feature articles: each has unique styling -->
    <iframe src="articles/fashion-feature.html" data-passthrough="false"></iframe>
    <iframe src="articles/architecture-feature.html" data-passthrough="false"></iframe>
    <iframe src="articles/graphic-design-feature.html" data-passthrough="false"></iframe>

    <!-- Editorial: uses magazine theme -->
    <iframe src="articles/editorial.html" data-passthrough="true"></iframe>
</body>
</html>

14. Financial Report with Regulatory Sections

Corporate report with external regulatory content:

<!DOCTYPE html>
<html>
<head>
    <title>Annual Financial Report</title>
    <style>
        body {
            font-family: 'Arial', sans-serif;
            color: #1a1a1a;
            font-size: 10pt;
            line-height: 1.5;
        }

        h1 {
            color: #003d7a;
            font-size: 18pt;
            border-bottom: 3pt solid #003d7a;
            padding-bottom: 10pt;
        }

        h2 {
            color: #0066cc;
            font-size: 14pt;
            margin-top: 25pt;
        }

        .financial-table {
            font-family: 'Courier New', monospace;
            font-size: 9pt;
        }
    </style>
</head>
<body>
    <h1>XYZ Corporation Annual Report 2024</h1>

    <!-- Company sections: use corporate theme -->
    <iframe src="sections/letter-to-shareholders.html" data-passthrough="true"></iframe>
    <iframe src="sections/business-overview.html" data-passthrough="true"></iframe>
    <iframe src="sections/financial-highlights.html" data-passthrough="true"></iframe>

    <!-- Regulatory sections: maintain original formatting -->
    <iframe src="regulatory/sec-filing.html" data-passthrough="false"></iframe>
    <iframe src="regulatory/audit-report.html" data-passthrough="false"></iframe>

    <!-- Company sections: use corporate theme -->
    <iframe src="sections/management-discussion.html" data-passthrough="true"></iframe>
    <iframe src="sections/future-outlook.html" data-passthrough="true"></iframe>
</body>
</html>

15. Debug and Comparison View

Compare styled vs. unstyled rendering:

<!DOCTYPE html>
<html>
<head>
    <title>Style Passthrough Comparison</title>
    <style>
        body {
            font-family: 'Verdana', sans-serif;
            color: #c0392b;
            font-size: 14pt;
            font-weight: bold;
        }

        h1 {
            color: #16a085;
            font-size: 24pt;
        }

        .comparison-container {
            display: flex;
            margin: 20pt 0;
        }

        .comparison-column {
            width: 50%;
            padding: 10pt;
            border: 1pt solid #ccc;
        }

        .label {
            font-size: 12pt;
            color: #333;
            font-weight: normal;
            margin-bottom: 10pt;
            padding: 5pt;
            background-color: #f0f0f0;
        }
    </style>
</head>
<body>
    <h1>Style Passthrough Comparison</h1>
    <p>Parent styles: Verdana 14pt Bold Red</p>

    <div class="comparison-container">
        <div class="comparison-column">
            <div class="label">With Passthrough (inherits parent)</div>
            <iframe src="test-content.html"
                    data-passthrough="true"
                    style="width: 100%; min-height: 200pt;"></iframe>
        </div>

        <div class="comparison-column">
            <div class="label">Without Passthrough (isolated)</div>
            <iframe src="test-content.html"
                    data-passthrough="false"
                    style="width: 100%; min-height: 200pt;"></iframe>
        </div>
    </div>
</body>
</html>