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### 9.5 Pipes

By typing `pipe` in front of a box definition, it is turned into a pipe. Pipes can represent tunnels, encapsulation or other associations (e.g., encryption) in networking technologies. Using them one can visually express as messages travel within the tunnels or along other associations.

Pipes take all the attributes of boxes, plus two extra ones, called `solid` and `side`. `solid` controls the transparency of the pipe. It can be set between 0 and 1 (or alternatively 0 and 255, similar to color RGB values). The value of 0 results in a totally transparent pipe: all its contents is drawn in front of it. The value of 1 results in a totally opaque pipe, all its content is "inside" the pipe, not visible. Values in between result in a semi-transparent pipe. `side` can be set to `left` or `right` and governs which side the pipe can be looked into from47.

For pipes the `line.radius` attribute governs, how wide the oval is at the two ends of the pipe. The default value is 5. Note that `line.corner` has no effect for pipes. Both `line.radius` and `side` can only be set on the first of the pipe segments, see below.

On the example above one can observe, that the last two pipes are smaller than the first two, even though they have exactly the same two arrows within. This is because in case of the first two arrows the label of the pipe itself is visible at together with the two arrows within. In contrast, the last two pipes are fully opaque so the pipe label can be drawn over its content.

Note the two `defstyle` commands before the pipes, as well. They are re-defining the default fill for pipes. You can read more about this in Defining Styles.

Similar to boxes multiple subsequent pipe definitions can be placed after each other without a semicolon. In case of boxes this results in a series of vertical connected boxes. In case of pipes this results in a series of horizontal pipe segments besides each other. However, contrary to boxes only one set of content can be specified.

#### Footnotes

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Beware that if you embed the chart in a Windows document, then using a lot of transparency can increase the size of the embedded object excessively.

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