|AllowDowngrades||YesNoType|| When set to no (the default), products with lower version numbers are blocked from installing when a product with a higher version is installed; the DowngradeErrorMessage attribute must also be specified.
When set to yes, any version can be installed over any other version.
|AllowSameVersionUpgrades||YesNoType|| When set to no (the default), installing a product with the same version and upgrade code (but different product code) is allowed and treated by MSI as two products. When set to yes, WiX sets the msidbUpgradeAttributesVersionMaxInclusive attribute, which tells MSI to treat a product with the same version as a major upgrade.
This is useful when two product versions differ only in the fourth version field. MSI specifically ignores that field when comparing product versions, so two products that differ only in the fourth version field are the same product and need this attribute set to yes to be detected.
Note that because MSI ignores the fourth product version field, setting this attribute to yes also allows downgrades when the first three product version fields are identical. For example, product version 184.108.40.206 will "upgrade" 220.127.116.1198 because they're seen as the same version (1.0.0). That could reintroduce serious bugs so the safest choice is to change the first three version fields and omit this attribute to get the default of no.
This attribute cannot be "yes" when AllowDowngrades is also "yes" -- AllowDowngrades already allows two products with the same version number to upgrade each other.
|Disallow||YesNoType|| When set to yes, products with higer version numbers are blocked from installing when a product with a lower version is installed; the UpgradeErrorMessage attribute must also be specified.
When set to no (the default), any version can be installed over any lower version.
|DisallowUpgradeErrorMessage||String||The message displayed if users try to install a product with a higer version number when a product with a lower version is installed. Used only when Disallow is yes.|
|DowngradeErrorMessage||String||The message displayed if users try to install a product with a lower version number when a product with a higher version is installed. Used only when AllowDowngrades is no (the default).|
|IgnoreRemoveFailure||YesNoType|| When set to yes, failures removing the installed product during the upgrade will be ignored.
When set to no (the default), failures removing the installed product during the upgrade will be considered a failure and, depending on the scheduling, roll back the upgrade.
|MigrateFeatures||YesNoType|| When set to yes (the default), the MigrateFeatureStates standard action will set the feature states of the upgrade product to those of the installed product.
When set to no, the installed features have no effect on the upgrade installation.
|RemoveFeatures||String||A formatted string that contains the list of features to remove from the installed product. The default is to remove all features. Note that if you use formatted property values that evaluate to an empty string, no features will be removed; only omitting this attribute defaults to removing all features.|
|Schedule||Enumeration|| Determines the scheduling of the RemoveExistingProducts standard action, which is when the installed product is removed. The default is "afterInstallValidate" which removes the installed product entirely before installing the upgrade product. It's slowest but gives the most flexibility in changing components and features in the upgrade product.
For more information, see RemoveExistingProducts. This attribute's value must be one of the following: