This is a short glossary of important terms in Leo’s world. For more information about terms, look in the index for links to discussions in other places, especially in Leo’s Tutorial and Leo’s Reference.


Starts a doc part. Doc parts continue until an @c directive or the end of the body text.
@@ convention for headlines
Within @asis trees only, if a headline starts with @@, Leo writes everything in the headline following the @@ just before the corresponding body text.
@<file> node
A node whose headline starts with @asis, @clean, @edit, @file, @shadow, @thin, or their longer forms. We often refer to outline nodes by the directives they contain. For example, an @file node is a node whose headline starts with @file, etc.
Copies the body text of all nodes in an @file tree to the external file.
@asis <filename>
Creates an external file containing no Leo sentinels directly from the @asis tree.

@auto <filename>

Imports an external file into the Leo outline, splitting the file into pieces if an importer exists for the give filetype. Importers presently exist for the following languages: C, C++, C#, HTML, INI files, Java, PHP, Pascal, Python and XML.

@c and @code

Ends a doc part and starts a code part.


An @chapter tree represents a chapter.


Creates an external file without sentinels. Section references and the @all and @others directives are valid in @clean trees.


Enables syntax coloring in a node and its descendants until the next @nocolor directive.


Sets the comment delimiters in @thin, @file and @shadow files.


Sets the comment delimiters in @thin, @file and @shadow files.

@edit <filename>

Reads an entire external file into a single node.

@encoding <encoding>

Specifies the Unicode encoding for an external file.


Ends a section of ‘raw’ text.

@file <filename>

Creates an external file containing sentinels. When writing @file trees, Leo expands section references and @all and @others directives. Important: @file is the recommended way to create and edit most files. Using @file trees is highly recommended when sharing external files in a collaborative environment.

@first <text>

The @first directive allows you to place one or more lines at the very start of an external file, before the first sentinel. The @first directive must appear at the very start of body text. For example:

@first #! /usr/bin/env python


Completely disables syntax coloring in a node, regardless of other directives.

@language <language name>

Specifies the source language, which affects syntax coloring and the comments delimiters used in external files and syntax coloring.

@last <text>

Allows you to place lines at the very end of external files, after the last sentinel. This directive must appear at the very end of body text. For example:

@first <?php
@last ?>

@lineending cr/lf/nl/crlf

Sets the line endings for external files.


Disables syntax coloring in a node and its descendants until the next @color directive.


Completely disables coloring for one node. Descendant nodes are not affected.


Creates external files without sentinels. Unlike @clean, @nosent trees are never updated from from external files.


Disables line wrapping the Leo’s body pane.


Copies the body text of all nodes except section definition nodes in an @file tree to the corresponding external file.

@pagewidth <n>

Sets the page width used to break doc parts into lines.
Starts a section of “raw” text that ends only with the @end_raw directive or the end of the body text.

@tabwidth <n>

Sets the width of tabs. Negative tab widths cause Leo to convert tabs to spaces.

@thin <filename>

A synonym for @file.


Enables line wrapping in Leo’s body pane.

A - C

Body pane

The pane containing the body text of the currently selected headline in the outline pane.

Body text

The text in the body pane. That is, the contents of a node.

Body text box

A small blue box in the icon box indicating that the node contains body text.


The direct descendant of a node.
A copy of a tree that changes whenever the original changes. The original and all clones are treated equally: no special status is given to the “original” node.

Clone arrow

A small red arrow in the icon box indicating that the node is a clone.

Code part

A part of a section definition that contains code. Code parts start with @c or @code directives and continue until the next doc part.


To hide all descendants of a node.

D - G

To move all siblings that follow a node so that they become children of the node.
An offspring of a node. That is, a child, grandchild, etc. of a node.


A keyword, preceded by an ‘@’ sign, in body text that controls Leo’s operation. The keyword is empty for the @ directive.

Dirty Node

A node whose headline or body text has changed.

Doc part

A part of a section definition that contains comments. Doc parts start with @ and continue until the @c directive or the end of the body text.

Escape convention

A convention for representing sequences of characters that would otherwise have special meaning. Important: Leo does not support escape conventions used by noweb. Any line containing matched << and >> is a section reference, regardless of context. To use << and >> as ordinary characters, place them on separate lines.


To make the children of a node visible.

External file

A file outside of Leo that is connected to Leo by an @<file> node.

Gnx (Global Node Index)

A unique, immutable string permanently associated with each vnode. See format of external files.


The child of a child of a node.

H - L


The headline text of a node. The part of the node visible in the outline pane.

Hoist & dehoist

Hoisting a node redraws the screen that node and its descendants becomes the only visible part of the outline. Leo prevents the you from moving nodes outside the hoisted outline. Dehoisting a node restores the outline. Multiple hoists may be in effect: each dehoist undoes the effect of the immediately preceding hoist.

Icon box

An icon just to the left of headline text of a node indicating whether the node is cloned, marked or dirty, and indicating whether the node contains body text.

Log Pane

The part of Leo’s main window that shows informational messages from Leo. It also contains the Find tab, the Spell tab, the autocompletion tab.

M - O


A red vertical line in the icon box of a node.


The organizational unit of an outline. The combination of headline text and body text. Sometimes used as a synonym for tree.


A synonym for the descendants of a node. The children, grandchildren, etc. of a node.

Organizer node

A node containing no body text. Organizing nodes may appear anywhere in an @file tree; they do not affect the external file in any way. In particular, organizing nodes do not affect indentation in external files.

Orphan node

A node that would not be copied to a external file. Orphan nodes can arise because an @file tree has no @others or @all directives. Sections that are defined but not used also create orphan nodes.

Leo issues a warning when attempting to write an @file tree containing orphan nodes, and does not save the external file. No information is lost; Leo saves the information in the @file tree in the .leo file. Leo will load the @file tree from the .leo file the next time Leo opens the .leo file.


A node and its descendants. A tree. All the nodes of a .leo file.

Outline order

The order that nodes appear on the screen when all nodes are expanded.

Outline pane

The pane containing a visual representation of the entire outline, or a part of the outline if the outline is hoisted.

P - R


The node that directly contains a node.


A way to modify and extend Leo without changing Leo’s core code. See Writing plugins and hooks.


To move all children of a node in an outline so that they become siblings of the node.

Reference .leo file

Leo’s git repository and Leo distributions contain the following reference files: LeoPyRef.leo, LeoPluginsRef.leo and leoGuiPluginsRef.leo. These reference files should contain nothing but @file nodes and should change only when new external files get added to the project. Developers should use local copies of reference files for their own work. For example, instead of using LeoPyRef.leo directly, I use a copy called LeoPy.leo.

reStructuredText (rST)

A simple, yet powerful markup language for creating .html, or LaTeX output files. See the rST primer.


The first node of a .leo file, outline, suboutline or @<file> tree.

S - Z


A fragment of text that can be incorporated into external files.

Section definition

The body text of a section definition node.

Section definition node

A node whose headline starts with a section name and whose body text defines a section.

Section name

A name enclosed in << and >>. Section names may contain any characters except newlines and “>>”.

Section reference

A section name appearing in a code part. When writing to an external file, Leo replaces all references by their definitions.


Comment lines in external files used to represent Leo’s outline structure. Such lines start with an @ following the opening comment delimiter. Sentinels embed outline structure into external files.

Do not alter sentinel lines. Doing so can corrupt the outline structure.


Plugins and other parts of Leo can get options from @settings trees, outlines whose headline is @settings. When opening a .leo file, Leo looks for @settings trees in the outline being opened and also in various leoSettings.leo files. @settings trees allow plugins to get options without any further support from Leo’s core code. For a full discussion of @settings trees, see Customizing Leo.


Nodes with the same parent. Siblings of the root node have the hidden root node as their parent.

Target language

The language used to syntax color text. This determines the default comment delimiters used when writing external files.


An outline. A node and its descendants.

Underindent line

A line of body text that is indented less then the starting line of the class, method or function in which it appears. Leo outlines can not represent such lines exactly: every line in an external file will have at least the indentation of any unindented line of the corresponding node in the outline.


uA’s (User Attributes) are persistent Python dicts that allows scripts and plugins to associate additional data with each node. See extensible attributes.

View node

A node that represents a view of an outline. View nodes are typically ordinary, non-cloned nodes that contain cloned descendant nodes. The cloned descendant nodes comprise most of the data of the view. Other non-cloned nodes may add additional information to the view.