仕様書

[1] content attribute | content property (Internet Explorer) (2012-11-18 02:23:20 +09:00 版) http://msdn.microsoft.com/en-us/library/ms533689(VS.85).aspx

値

noopen
Internet Explorer 6 for Windows XP SP2 and later. Hides the Open or Run button on the File Download dialog box. This value requires the name attribute to be set with the DownloadOptions value.
nosave
Internet Explorer 6 for Windows XP SP2 and later. Hides the Save button on the File Download dialog box. This value requires the name attribute to be set with the DownloadOptions value.

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例

[3]

<meta name="DownloadOptions" content="noopen">

関連

[2] 後に noopen に相当する機能として X-Download-Options: が導入されています。