src/context.js
function writeTop(d, loc) {
            if (d.indexOf('\n') != -1) {
                throw 'Can not write content having \\n'
            }
            this.chunks.unshift(chunk(d, loc))
        }
function writeTop(d, loc) {
            if (d.indexOf('\n') != -1) {
                throw 'Can not write content having \\n'
            }
            this.chunks.unshift(chunk(d, loc))
        }
unshift a new chunk