Gets or sets the outline level of a paragraph.
An integer specifying the level number, or null to indicate a mix of values.
Outline levels are used to build a table of contents without changing the appearance of your text.
When a document is exported to HTML with default settings, the outline level specifies the tag in which the paragraph is enclosed. Outline levels from1 to 6 result in H1 - H6 tags respectively; paragraphs with outline levels higher than 6 are exported as text enclosed in a P tag. You can set the HtmlDocumentExporterOptions.IgnoreParagraphOutlineLevel option to true to export all paragraphs using only <P> tags, disregarding their outline levels.