A table column in Layout mode can have either a fixed width or a width that automatically expands to fill as much of the browser window as possible (autostretch).

Fixed-width columns

Have a specific numeric width, such as 300 pixels. Dreamweaver displays the column width for each fixed-width column at the top or bottom of the column.

Autostretch columns

Change automatically depending on the browser window’s width. If your layout includes an autostretch column, the layout always fills the entire width of the visitor’s browser window. You can make only one column in a given layout table autostretch. An autostretch column displays a wavy line in the column width area.

A common layout is to make the column containing the main content of the page autostretch, which automatically sets all the other columns to fixed width. For example, suppose your layout has a wide image on the left side of the page and a column of text on the right. You might set the left column to a fixed width and make the sidebar area autostretch.

When you make a column autostretch, Dreamweaver inserts spacer images in the fixed width columns to ensure that those columns stay as wide as they should be, unless you specify that no spacer image should be used. A spacer image is a transparent image, used to control spacing, that is not visible in the browser window.