0 - Do not report any conditions.
1 - Report only conditions where significant information content has been changed. For instance, an unsupported time-scale has been replaced by a supported near-equivalent time-scale. Another example is if a basic Channel unexpected encounters data items that may have been introduced by later versions of AST.
2 - Report the above, and in addition report significant default values. For instance, if no time-scale was specified when reading an Object from an external data source, report the default time-scale that is being used.
3 - Report the above, and in addition report any other potentially interesting conditions that have no significant effect on the conversion. For instance, report if a time-scale of "TT" (terrestrial time) is used in place of "ET" (ephemeris time). This change has no signficiant effect because ET is the predecessor of, and is continuous with, TT. Synonyms such as "IAT" and "TAI" are another example.
The default value is 1. Note, there are many other conditions that can occur whilst reading or writing an Object that completely prevent the conversion taking place. Such conditions will always generate errors, irrespective of the ReportLevel and Strict attributes.
AST A Library for Handling World Coordinate Systems in Astronomy