Add information about the differences between CSV export and import formats.

docs/guide/export.md

@@ -6,7 +6,71 @@ bottom that will generate and download a CSV file.
 Any sorts or filters that are applied to the list will be represented in the
 CSV output.
 
+## Reimporting
+
+**While it is technically possible to move data from one farmOS to another via
+CSV files, it is not recommended due to differences in the import/export CSV
+format.**
+
+If you are trying to export assets or logs from one farmOS site so that they
+can be imported into another farmOS site it is important to note that there are
+some differences that can complicate things. It is technically possible, but
+there are some limitations and differences to be aware of. Please read all of
+the following before attempting it.
+
+There is an open issue to resolve these differences here:
+[https://www.drupal.org/node/2900239](https://www.drupal.org/node/2900239)
+
+### Differences and considerations
+
+Some of the differences and considerations to be aware of are described below.
+
+#### Column differences
+
+In most cases, the CSV column names that are exported from asset and log lists
+will match those of the corresponding [CSV importer] for that type. There may
+be columns present in imports that are not present in exports, and vice versa.
+Compare the exported CSV columns to the importer's CSV template columns before
+importing to understand what pieces of information might be missing from either
+side.
+
+#### Asset and log IDs
+
+Exported CSVs will include a column for the asset or log ID, which is not
+available as a field for import. You can still import CSVs with this column,
+but it will be ignored during the import and a new ID will be assigned by
+farmOS to the imported asset or log. If there are any other logs or assets that
+reference this ID, they will need to be manually updated to point to the
+correct IDs when you import them.
+
+#### Log "Done" column
+
+In log exports, the "Done" column will contain a checkmark if the log is done,
+and it will be empty if the log is not done. This differs from the format
+expected by log importers. Log importers expect a value of "yes" or "no" in the
+"Done" column, and blank values will automatically default to "yes", which is
+the opposite of what a blank value means in CSV exports.
+
+#### Truncated text
+
+Descriptions, notes, and other long text fields are truncated when they are
+displayed in asset and log lists in farmOS. When those lists are exported to
+CSV, the text will also be truncated in the export.
+
+#### Files and images
+
+CSV exports do not provide any mechanism for exporting images or files that are
+attached to assets or logs. Files and images need to be uploaded manually after
+import.
+
+#### Asset location
+
+The CSV importers provided for assets do not currently support setting asset
+location, and log importers do not currently support importing movement
+information. Asset location needs to be set manually after assets are imported.
+
 [asset]: /guide/assets
 [log]: /guide/logs
 [CSV]: https://en.wikipedia.org/wiki/Comma-separated_values
+[CSV importer]: /guide/import