added in docs and NEWS

NEWS.md

@@ -7,6 +7,8 @@ shiny 1.3.2.9000
 
 ### Improvements
 
+* Resolved [#612](https://github.com/rstudio/shiny/issues/612): An optional paramter `alt` can be passed to `renderPlot()` and `renderCachedPlot()`, which is then added to the img-tag.
+
 * Resolved [#2402](https://github.com/rstudio/shiny/issues/2402): An informative warning is now thrown for mis-specified (date) strings in `dateInput()`, `updateDateInput()`, `dateRangeInput()`, and `updateDateRangeInput()`. ([#2403](https://github.com/rstudio/shiny/pull/2403))
 
 * Resolved [#2442](https://github.com/rstudio/shiny/issues/2442): The `shiny:inputchanged` JavaScript event now triggers on the related input element instead of `document`. Existing event listeners bound to `document` will still detect the event due to event bubbling. ([#2446](https://github.com/rstudio/shiny/pull/2446))

R/render-cached-plot.R

@@ -146,6 +146,7 @@
 #'   possible pixel dimension. See \code{\link{sizeGrowthRatio}} for more
 #'   information on the default sizing policy.
 #' @param res The resolution of the PNG, in pixels per inch.
+#' @param alt Optional parameter to pass `alt` to the img-tag.
 #' @param cache The scope of the cache, or a cache object. This can be
 #'   \code{"app"} (the default), \code{"session"}, or a cache object like
 #'   a \code{\link{diskCache}}. See the Cache Scoping section for more

R/render-plot.R

@@ -30,6 +30,7 @@
 #' @param res Resolution of resulting plot, in pixels per inch. This value is
 #'   passed to \code{\link[grDevices]{png}}. Note that this affects the resolution of PNG
 #'   rendering in R; it won't change the actual ppi of the browser.
+#' @param alt Optional parameter to pass `alt` to the img-tag.
 #' @param ... Arguments to be passed through to \code{\link[grDevices]{png}}.
 #'   These can be used to set the width, height, background color, etc.
 #' @param env The environment in which to evaluate \code{expr}.