The oxy_substring() Function

The oxy_substring() function is used to return a string of text.

The oxy_substring() function has two signatures:

oxy_substring('abcd', 1) returns the string 'bcd'.

oxy_substring('abcd', 4) returns an empty string.

oxy_substring('abcd', 1, 3) returns the string 'bc'.

If we want to display only part of an attribute's value, the part which comes before an Appendix string:
image[longdesc]{
 content: oxy_substring(attr(longdesc), 0, oxy_indexof(attr(longdesc), "Appendix"));
}