unexpected character sequence in member name in a json document

I have a json document that looks more or less like this:

[
{
attr11:"value11",
attr12:"value12"
},
{
attr21:"value21",
attr22:"value22"
},
{
attr31:"value31",
attr32:"value32"
}
]

Visual Studio underlines the first letters of attrN and says "unexpected character sequence in member name". What is that?