This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
How to | Identify Different Cell Brackets
 Content in a Mathematica notebook is organized in cells. Each cell has a cell bracket that appears along the right edge of the notebook window. Markings on a cell bracket indicate important information about that cell.
This is a selection of examples from the complete "How to" screencast. »
All cell brackets have the same basic outline, specifically, a vertical line bordered by shorter horizontal lines at the top and bottom.
Look to the right edge of this window to see the cell brackets of the input and output cells in this simple calculation:
 Out[2]=
If you just start typing in a typical Mathematica notebook, you will see a cell bracket with a triangular notch at the top. These cells can contain typeset Mathematica expressions and can be evaluated:
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A cell that cannot be evaluated will have a second horizontal line near the top of its cell bracket, such as this text cell:
A cell can also be marked as an initialization cell. Initialization cells are evaluated automatically before you evaluate other cells in the notebook. An initialization cell has a short vertical bar at the top of its cell bracket:
A cell in the Code cell style is automatically marked as an initialization cell:
`g[x_]:=x3+x2+1`
A cell with a dashed line down the whole height of the cell bracket is a TraditionalForm cell. TraditionalForm cells contain typeset formulas that might be ambiguous if they were to be interpreted as Mathematica expressions:
Evaluating a cell that contains a syntax error will add an error indication to the cell bracket, indicating a problem with the cell's content. You can click on the indicator to show the error messages, as was done in this screen shot:
Other cell bracket annotations include the letter A to indicate that a cell is active, the letter X to indicate that editing is not allowed in that cell, or a filled square to indicate that the CellSize option is set.

Some brackets are not used for individual cells, but instead to collect groups of cells.
The larger outer bracket here joins these input and output cells into a group. Mathematica groups input and output cells by default:
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Cell groups can be closed by double-clicking the grouping bracket. The grouping bracket here was double-clicked to close the group. The direction of the arrow that appears on the grouping bracket indicates the direction of any hidden cells:
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A cell group can also be closed by double-clicking the bracket of the first cell in that group. Note that this produces the same result as double-clicking the grouping bracket:
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Double-clicking the bracket of an output cell will hide the input cell that produced it. This is useful if you want to keep the input for future use or reference, but do not need to view it all the time.
Here, the bracket of the output cell containing was double-clicked to hide the input cell containing . Note the arrow on the grouping bracket points up to indicate the direction of the hidden input cell:
 Out[8]=
To open a closed cell group, simply double-click the grouping bracket with the arrow.