There are different types of inputs that are allowed for a parameter - 
Defined by giving value to label attribute.
- Slider Input  
 
- Numerical/ date/ text Input
 
- Password Input
 
- select list
 
- radio buttons
 
- file input
 
All the types follow the same syntax for defining the parameter.
title: sample
output: html_document
params:
  year:
    label: "Year"
    value: 2017
    input: slider
    min: 2010
    max: 2018
    step: 1
    sep: ""
---
The attributes change depending on the type of input such as value, sep.min,max ,etc.