These are all the possible values for the IG_ISIS_TAG_OPENATTRIBUTE tag.
Values:
| IG_ISIS_FILE_READ | Open file for read access. |
| IG_ISIS_FILE_WRITE | Open file for write access. |
| IG_ISIS_FILE_BOTH | Open file for read/write access. |
| IG_ISIS_OPENATTRIBUTE_CREATE | Create file if it doesn't exist. |
| IG_ISIS_OPENATTRIBUTE_DONTOPEN | Don't open existing file. |
| IG_ISIS_OPENATTRIBUTE_CREATEONLY | Only create a new file - fail if it already exists. |
| IG_ISIS_OPENATTRIBUTE_IFFLAGS | OR of all special flags. |