If no Format value is set for a Frame axis, a default value is supplied instead. This is based on the value of the Digits, or Digits(axis), attribute and is chosen so that it displays the requested number of digits of precision.
When supplying a value for this attribute, beware that the "%" character may be interpreted directly as a format specification by some printf-like functions (such as astSet). You may need to double it (i.e. use "%%") to avoid this.
All of the above format specifiers are case-insensitive. If several characters make conflicting requests (e.g. if both "i" and "b" appear), then the character occurring last takes precedence, except that "d" and "h" always override "t".
AST A Library for Handling World Coordinate Systems in Astronomy