GetElementAttr() does not consider all elements in input MEI file

[GustavTaxen]

It looks like vrv::Toolkit::GetElementAttr() only returns certain types of element. For example, <staffDef> elements cannot be queried, which makes it impossible to use the Toolkit to find the meter count and unit for a staff.

To reproduce, load a MEI file with an identified <staffDef> element, e.g.,

...
<scoreDef>
  <staffGrp>
    <staffDef xml:id="mystaff" n="1" lines="5" clef.shape="F" clef.line="4" meter.count="4" meter.unit="4" />
  </staffGrp>
</scoreDef>
...

Expected behaviour
The function searches all elements for the specified xml:id tag. In this case, it should return an object that contains

{
	"n": "1",
	"lines": "5",
	"clef.shape": "F",
	"clef.line": "4",
	"meter.count": "4",
	"meter.unit": "4"
}

Actual behaviour
The function returns {}, an empty object.

Verovio information

• Version of Verovio: 4.2.0
• Binding: JavaScript

Environment information (as appropriate)

• OS: MacOS
• Browser: Chrome