[GitHub] [arrow] jonkeane commented on a change in pull request #11972: ARROW-15022: [R] install vignette and installation dev vignette need alt text for images

[GitBox <gi...@apache.org>]

jonkeane commented on a change in pull request #11972:
URL: https://github.com/apache/arrow/pull/11972#discussion_r770582055



##########
File path: r/vignettes/developers/install_details.Rmd
##########
@@ -57,23 +57,31 @@ correct components are described below.
 
 The diagram below shows how the R package finds a libarrow installation on Windows.
 
-```{r, echo=FALSE, out.width="70%"}
+```{r, echo=FALSE, out.width="70%", fig.alt = "Flowchart of libarrow installation on Windows systems - find full description on page"}

Review comment:
       Would you mind adding the full subheader title to this alt text? That way it would be a little bit easier to skim with a screen reader and then get the heading one wants?

##########
File path: r/vignettes/developers/install_details.Rmd
##########
@@ -57,23 +57,31 @@ correct components are described below.
 
 The diagram below shows how the R package finds a libarrow installation on Windows.
 
-```{r, echo=FALSE, out.width="70%"}
+```{r, echo=FALSE, out.width="70%", fig.alt = "Flowchart of libarrow installation on Windows systems - find full description on page"}
 knitr::include_graphics("./install_diagram_windows.png")
 ```
 
-### Linux
+#### Checking for existing libarrow installations
+
+When you install the arrow R package on Windows, if the `ARROW_HOME` environment variable has not been set, the install script looks for an existing libarrow installation.  If this cannot be find, it then checks whether the `R_WINLIB_LOCAL` environment variable has been set to point to a local installation.
+
+#### Downloading libarrow
+
+If no existing libarrow installations can be found, the script proceeds to try to download the required version of libarrow, first from the nightly builds repository and then from Rwinlib.  The script first tries to find a version of libarrow which is matches the most components according to semantic versioning, and in the case of a failure becomes less specific (i.e. if there are no binaries found for version 0.14.1.1, then try to find one for 0.14.1).
+
+### Non-Windows
 
 The diagram below shows how the R package finds a libarrow installation on non-Windows systems.
 
-```{r, echo=FALSE, out.width="70%"}
+```{r, echo=FALSE, out.width="70%", fig.alt = "Flowchart of libarrow installation on non-Windows systems - find full description on page"}

Review comment:
       Same here




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