function solve () {
     return function (selector) {
	 function isHTMLElement(obj){
                return obj === 'object' && obj instanceof HTMLElement;
        }

        function isString(obj){
                return obj === 'string' || obj instanceof String;
        }

        function isExistingId(id){
                var element = document.getElementById('id');
                return element !== 'undefine' && element !== null;
        }

        var validator = {
                validateParams: function (selector){
                        if(!isString(selector) && !isHTMLElement(selector)){
                                throw new Error('The provided id is not a string or does not select any DOM element!');
                        }
                }

                validateExistingId: function (id){
                        if (!isExistingId(id)) {
                                throw new Error('The provided id does not select anything!');
                        }
                }
        }
                // Validations
                validator.validateParams(selector);
                validator.validateExistingId(selector);

                // Select all buttons and change their content to 'hide'
                var buttons = document.getElementsByClassName('button'),
                        i,len;

                for(i = 0; len = buttons.length; i < len; i+=1){
                        buttons[i].innerHTML = 'hide';
                }

                // Iterate over all buttons and implement onclick functionality
                for(i = 0; len = buttons.length; i < len; i+=1){
                        var currButton = buttons[i];

                        currButton.addEventListener('click', function(ev){
                                var clickedButton = ev.target;
                                var nextContent = clickedButton.nextElementSibling;
                                while(nextContent && nextContent.className.indexOf('content') < 0){
                                        nextContent = nextContent.nextElementSibling;
                                }

                                var isContentVisible = nextContent.style.display === ''; // <=> display:block
                                if (isContentVisible) {
                                        nextContent.style.display = 'none';
                                        clickedButton.innerHTML = 'show';
                                }else{
                                        nextContent.style.display = ''; // <=> display:block
                                        clickedButton.innerHTML = 'hide';
                                }

                        });

                }
        }
}