Formatting service

    Apply character and paragraph formatting to the current editor selection. Use these operations for application-owned formatting controls.

    The facade is available as editor.Formatting; its interface can be replaced by an application implementation.

    A selected project heading centered in Avalonia HTML Editor, with its bold and alignment state reflected in the toolbar.
    A selected project heading centered in Avalonia HTML Editor, with its bold and alignment state reflected in the toolbar.

    Use it in your application

    Formatting requires an appropriate editable selection or caret. Source mode supports the documented literal wrapping and insertion adaptations; it is not a hidden Design selection.

    All examples assume an editor named editor, already attached to a visible window, and an awaited editor.Ready. Keep operations asynchronous instead of blocking the UI thread.

    await editor.Formatting.BoldAsync();
    await editor.Formatting.ChangeFontSizeAsync("12pt");
    

    Members

    These declarations come from the package's own XML documentation. Await operations and supply cancellation tokens where your application needs them.

    AlignCenterAsync Method

    Centers the current design selection.

    Syntax
    Task AlignCenterAsync(CancellationToken cancellationToken = default)
    

    AlignLeftAsync Method

    Aligns the current design selection to the left.

    Syntax
    Task AlignLeftAsync(CancellationToken cancellationToken = default)
    

    AlignRightAsync Method

    Aligns the current design selection to the right.

    Syntax
    Task AlignRightAsync(CancellationToken cancellationToken = default)
    

    ApplyListAsync Method

    Sets, clears or toggles the requested list format in design mode.

    Syntax
    Task ApplyListAsync(ListTypes listType, FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    ApplyTitleHeaderAsync Method

    Applies heading level 1 through 6, or a paragraph for level 0.

    Syntax
    Task ApplyTitleHeaderAsync(int headerNumber, CancellationToken cancellationToken = default)
    

    BoldAsync Method

    Sets, clears or toggles bold on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task BoldAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    ChangeFontAsync Method

    Applies font family, CSS size and native color together to the current design selection.

    Syntax
    Task ChangeFontAsync(string fontFamilyName, string fontSize, Color foreColor, CancellationToken cancellationToken = default)
    

    ChangeFontNameAsync Method

    Applies a font family to the current design selection.

    Syntax
    Task ChangeFontNameAsync(string fontFamilyName, CancellationToken cancellationToken = default)
    

    ChangeFontSizeAsync Method

    Applies the supplied CSS font size and unit to the current design selection.

    Syntax
    Task ChangeFontSizeAsync(string fontSize, CancellationToken cancellationToken = default)
    

    ChangeForeColorAsync Method

    Applies a native foreground color to the current design selection.

    Syntax
    Task ChangeForeColorAsync(Color foreColor, CancellationToken cancellationToken = default)
    

    ChangeHighlightColorAsync Method

    Applies a native highlight color to the current design selection.

    Syntax
    Task ChangeHighlightColorAsync(Color highlightColor, CancellationToken cancellationToken = default)
    

    IndentAsync Method

    Increases indentation of the current design selection.

    Syntax
    Task IndentAsync(CancellationToken cancellationToken = default)
    

    ItalicAsync Method

    Sets, clears or toggles italic on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task ItalicAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    OutdentAsync Method

    Decreases indentation of the current design selection.

    Syntax
    Task OutdentAsync(CancellationToken cancellationToken = default)
    

    RemoveAlignmentAsync Method

    Removes authored alignment from selected design blocks.

    Syntax
    Task RemoveAlignmentAsync(CancellationToken cancellationToken = default)
    

    RemoveFormatAllAsync Method

    Resets the complete writable design body in one undo operation, preserving the shared reserved tags, their attributes and canonical field/video atoms. Source and preview are rejected.

    Syntax
    Task RemoveFormatAllAsync(CancellationToken cancellationToken = default)
    

    RemoveFormatFromSelectionAsync Method

    Removes inline formatting from the current design selection.

    Syntax
    Task RemoveFormatFromSelectionAsync(CancellationToken cancellationToken = default)
    

    RemoveHeaderTitleAsync Method

    Changes the selected heading to a paragraph.

    Syntax
    Task RemoveHeaderTitleAsync(CancellationToken cancellationToken = default)
    

    StrikeThroughAsync Method

    Sets, clears or toggles strike through on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task StrikeThroughAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    SubscriptAsync Method

    Sets, clears or toggles subscript on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task SubscriptAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    SuperscriptAsync Method

    Sets, clears or toggles superscript on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task SuperscriptAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    UnderlineAsync Method

    Sets, clears or toggles underline on the design selection, or wraps the source selection with its matching paired tag.

    Syntax
    Task UnderlineAsync(FormatOptions option = FormatOptions.Toggle, CancellationToken cancellationToken = default)
    

    Related guides

    Last updated on Oct 30, 2026

    Put this into practice.

    Start with the C# Avalonia sample. Restore this edition's package and install the native browser prerequisites before running it.

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