(a ? b : c) means (if a then b else c). The line is a nested if-else construct: if l is static string (?) then src = l->val_str else if l is a string buf

(a ? b : c) means (if a then b else c). The line is a nested if-else construct: if l is static string (?) then src = l->val_str else if l is a string buffer then src = l->val_strb_cstr + l->strb_off else src = l->val_chr