replace for a_text from old_text by new_text
The method should be called between store_delimiters() and restore_delimiters()
Parameters
- a_text (text or XText) :
a text to process
- old_text (text or XText) :
a text should be replaced by new_text
- new_text (text or XText) :
a text should be placed instead of old_text
Result
text : a text replacing old_text with new_text