XML tag name cannot start with a digit. From spec:
The first character of a Name must be a NameStartChar
NameStartChar ::= ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] |
[#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] |
[#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] |
[#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] |
[#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
So you need to manually escape character somehow before using it as a first character in tag name. For example, you can use underscore character if you don't have normal tags starting with it.