There is a serious bug in ExtJS 6.7, 7.0 in the Writer.Xml class I think.

For example, I edit a record and my text field contains '<' or '>' symbols.

Then I try to save this changed record to my database but I receive an error parsing xml document because XML Writer does not escapes special characters (i.e. '<' or '>' as &lt; or &gt when it send the data to the server.

Please see Ext.data.writer.Xml functions writeRecords() and objectToElement(), there is something like

else {
  subOutput.push('<', key, '>', datum, '</', key, '>');

so if we have some special characters in the datum variable we will have parsing xml errors.

I found a discussion about similar problem here