[Decoding] Accidental not decoding properly

[jsbean]

The Accidental structure is defined in MusicXML as:

<!ELEMENT accidental (#PCDATA)>
<!ATTLIST accidental
    cautionary %yes-no; #IMPLIED
    editorial %yes-no; #IMPLIED
    %level-display;
    %print-style;
    %smufl;
>

An example of this in the wild is:

<accidental editorial="yes" cautionary="yes">flat</accidental>

Due to CoreOffice/XMLCoder#12, elements which have both values (e.g., the #PCDATA which is "sharp", "flat", etc.) and attributes (e.g., cautionary, editorial) are not yet decodable.