The conditional formatting feature allows you to apply formats to a cell or range of cells, and have that formatting change depending on the value of the cell or the value of a formula. The Expression property specifies a formula that indicates the criteria to format the items or the columns. Use the ApplyTo property to specify when the items or the columns are  formatted. Use the Add method to specify the expression at adding time. The Expression property may include variables, constants, operators or ( ) parenthesis.  A variable is defined as %n, where n is the index of the column ( zero based ). For instance, the %0 indicates the first column, the %1, indicates the second column, and so on.  A constant is a float expression ( for instance, 23.45 ). Use the Valid property checks whether the expression is syntactically correct, and can be evaluated. If the expression contains a variable that is not known, 0 value is used instead. For instance, if your control has 2 columns, and the expression looks like "%2 +%1 ", the %2 does not exist, 0 is used instead. When the control contains two columns the known variables are %0 and %1. 

The expression may be a combination of variables, constants, strings, dates and operators.  A string is delimited by ", ` or ' characters, and inside they can have the starting character preceded by \ character, ie "\"This is a quote\"". A date is delimited by two # characters, ie #1/31/2001 10:00# means the January 31th, 2001, 10:00 AM.

The expression supports cell's identifiers as follows:

• %0, %1, %2, ...{any} specifies the value of the cell in the column with the index 0, 1 2, ... The CellCaption property defines the cell's value. For example, "%0 format ``" formats the value in the cell at index 0 using the current regional settings, while "int(%1)" converts the value in the cell at index 1 to an integer.
• %C0, %C1, %C2, ...{string} specifies the caption of the cell, or the string the cell displays in the column with the index 0, 1 2, ... The CellCaption property gets the cell's formatted caption. The cell's displayed string may differ from its actual value. For example, if a cell displays HTML content, %0 returns the HTML format including the tags, while %C0 returns the cell's content as a plain string without HTML tags. For instance, "upper(%C1)" converts the caption of the cell at index 1 to uppercase, while "%C0 left 2" returns the leftmost two characters of the caption in the cell at index 0.
• %CD0, %CD1, %CD2, ...{any} specifies the cell's extra data in the column with the index 0, 1 2, ... The CellData property associates any extra/user data to a cell. For example, "%CD0 = your user data" specifies all cells in the column with index 0 whose CellData property is equal to your user data.
• %CS0, %CS1, %CS2, ...{number} specifies the cell's state in the column with the index 0, 1 2, ... The CellState property defines the state of a cell, indicating whether it is checked or unchecked. For example, "%CS0" identifies all checked items in the column with index 0, while "not %CS1" identifies all unchecked items in the column with index 1.
• %CT0, %CT1, %CT2, ... {boolean} returns true if the cell displays a total field; otherwise, it returns false. The exTotalField / exTotalColumn flag specifies whether the cell displays a total field. For instance, "%CT1" refers to all cells in the second column that display totals, while "not %CT1" refers to all cells in the second column that do not display totals.
• %CE0, %CE1, %CE2, ... {boolean} returns true if the cell is editable; otherwise, it returns false.. For example, "%CE0" refers to all editable cells in the first column, while "not %CE1" refers to all cells in the second column that are read-only.
• %CC0, %CC1, %CC2, ... {number} retrieve the number of child items (this keyword consistently returns identical results for all cells since it pertains to the item that hosts each cell). The ChildCount property returns the number of child items. For example, "%CC0" identifies all parent items, while "%CC0 = 0" identifies all leaf items.
• %CX0, %CX1, %CX2, ... {boolean} returns true if the item hosting the cell is expanded, or false if it is collapsed (this keyword consistently returns identical results for all cells since it pertains to the item that hosts each cell). The ExpandItem property specifically indicates whether the item is expanded or collapsed. For example, "%CX0" refers to all expanded items, while "not %CX0" identifies all collapsed items

Usage examples:

• "1", highlights all cells or items. Use this form, when you need to highlight all cells or items in the column or control. 
• "%CC0 and %CX0", highlights items that are expanded and have children
• "%0 >= 0", highlights the cells or items, when the cells in the first column have the value greater or equal with zero
• "%0 = 1 and %1 = 0", highlights the cells or items, when the cells in the first column have the value equal with 0, and the cells in the second column have the value equal with 0 
• "%0+%1>%2", highlights the cells or the items, when the sum between first two columns is greater than the value in the third column
• "%0+%1 > %2+%3", highlights the cells or items, when the sum between first two columns is greater than the sum between third and forth column.
• "%0+%1 >= 0 and (%2+%3)/2 < %4-5", highlights the cells or the items, when the sum between first two columns is greater than 0 and the half of the sum between third and forth columns is less than fifth column minus 5.
• "%0 startwith 'A'", highlights cells that begin with "A"
• "%0 endwith 'Bc'", highlights cells that end with "Bc"
• "%0 contains 'aBc'", highlights cells that contain the string "aBc"
• "lower(%0) contains 'abc'", highlights cells that contain "abc", "AbC", "ABC", and similar variations
• "len(%0)>0" or "len(%0)", highlights non-blank cells
• "len(%0) = 0", highlights blank cells

This property supports auto-numbering (index, pos, ...) expressions as described here. This property/method supports predefined constants and operators/functions as described here.

The conditional format feature may change the cells and items as follows:

• Bold property. Bolds the cell or items
• Italic property. Indicates whether the cells or items should appear in italic.
• StrikeOut property. Indicates whether the cells or items should appear in strikeout.
• Underline property. Underlines the cells or items
• Font property. Changes the font for cells or items.
• BackColor property. Changes the background color for cells or items, supports skins as well.
• ForeColor property. Changes the foreground color for cells or items.

The following VB samples bolds all items when the sum between first two columns is greater than 0:

Tree1.ConditionalFormats.Add("%0+%1>0").Bold = True

The following C++ sample bolds all items when the sum between first two columns is greater than 0:

COleVariant vtEmpty;
m_tree.GetConditionalFormats().Add( "%0+%1>0", vtEmpty ).SetBold( TRUE );

The following VB.NET sample bolds all items when the sum between first two columns is greater than 0:

AxTree1.ConditionalFormats.Add("%0+%1>0").Bold = True

The following C# sample bolds all items when the sum between first two columns is greater than 0:

axTree1.ConditionalFormats.Add("%0+%1>0", null).Bold = true

The following VFP sample bolds all items when the sum between first two columns is greater than 0:

thisform.Tree1.ConditionalFormats.Add("%0+%1>0").Bold = .t.