This page discusses the non-native formats in which Opal can save an outline.
When you choose File > Save or File > Save As, Opal saves the document in its native format (as an .otln file). However, you can choose File > Export to save a copy of an Opal outline in some other format, possibly for purposes of display or exchange with some other program. Here are the formats as they are listed in the File Format popup menu in the Save dialog that appears when you choose File > Export:
Opal outline. This is Opal’s native format.
Text file. Three text file formats are listed; these correspond to three text encodings (UTF-8, MacRoman, and WinLatin-1 respectively). UTF-8 is a Unicode encoding and can express every character; MacRoman and WinLatin-1 represent limited character sets, so there is a possibility that your document will contain characters that cannot be saved in these formats (and if that is the case, Opal will refuse to do so).
In the exported document, every topic is treated as a paragraph. Outline indentation is represented by tab characters at the start of a paragraph: none for top-level topics, one for second-level topics, and so on. (Multi-paragraph topics are treated as separate topics of one paragraph each.) Text styling, pictures, and document links are stripped from the exported version of the document. Topic labels are represented as text at the start of a paragraph (followed by a space).
Rich Text Format (RTF). This is a plain text format containing styled text information. It is a format that many programs can read, including Microsoft Word and TextEdit. Tabs are used to represent levels of indentation, as in a text file (see above). Text styling is maintained; pictures and document links are stripped. Topic labels are represented as text at the start of a paragraph (followed by a space).
Rich Text With Graphics (RTFD). This is the only export format that preserves not only styled text but also pictures and document links. It is native to, and can be opened by, TextEdit. The outline is represented just as in an RTF file, except that pictures and links are visible. Internally, this format is actually a bundle — a folder that looks like a file. Inside that folder are copies of any pictures, along with alias files representing links.
HTML file. This is a text format suitable for display by a web browser. CSS is used to render indentation and text styling quite faithfully. Pictures are represented as <img> tags; these are just placeholders and will have to be edited manually if you want them to work in a browser. Document links are stripped. Topic labels are represented as text at the start of a paragraph (followed by a space).
Word file. This is a styled text format (.doc) that Microsoft Word and TextEdit can open. Features are equivalent to those of an RTF file (see above).
OPML outline. This is a plain text format using XML to express outline structure. It is a commonly used medium of exchange among outliners. Text styling, pictures, and document links are stripped. Topics consisting of multiple paragraphs are correctly expressed in this format.
After exporting with File > Export, the window still displays the original Opal document (and, if this document contained unsaved changes before the export, it still does).