没什么，就是document的一个方法而已，语法见内

差不多菜单的功能都可以用此命令实现。
Executes a command on the current document, current selection, or the given range.
Syntax
bSuccess = object.execCommand(sCommand [, bUserInterface] [, vValue])
Parameters
sCommand Required. String that specifies the command to execute. This command can be any of the command identifiers that can be executed in script.
bUserInterface Optional. Boolean that specifies one of the following values: false Default. Does not display a user interface.
true Displays a user interface, if the command supports one.

vValue Optional. Variant that specifies the string, number, or other value to assign. Possible values depend on sCommand .
Return Value
Boolean that returns one of the following values:
true The command was successful.
false The command was not successful.
Remarks
Do not invoke the execCommand method until after the page loads.
The bUserInterface and vValue parameters may be required depending on the command being executed.
Standards Information
There is no public standard that applies to this method.
Applies To