R: Preserve HTML regions

htmlPreserve {htmltools} | R Documentation

## Preserve HTML regions

### Description

Use "magic" HTML comments to protect regions of HTML from being modified by text processing tools.

### Usage

    htmlPreserve(x)

    extractPreserveChunks(strval)

    restorePreserveChunks(strval, chunks)

### Arguments

`x` | A character vector of HTML to be preserved.
`strval` | Input string from which to extract/restore chunks.
`chunks` | The `chunks` element of the return value of `extractPreserveChunks`.

### Details

Text processing tools like markdown and pandoc are designed to turn human-friendly markup into common output formats like HTML. This works well for most prose, but components that generate their own HTML may break if their markup is interpreted as the input language. The `htmlPreserve` function is used to mark regions of an input document as containing pure HTML that must not be modified. This is achieved by substituting each such region with a benign but unique string before processing, and undoing those substitutions after processing.

### Value

`htmlPreserve` returns a single-element character vector with "magic" HTML comments surrounding the original text (unless the original text was empty, in which case an empty string is returned).

`extractPreserveChunks` returns a list with two named elements: `value` is the string with the regions replaced, and `chunks` is a named character vector where the names are the IDs and the values are the regions that were extracted.

`restorePreserveChunks` returns a character vector with the chunk IDs replaced with their original values.

### Examples

    # htmlPreserve will prevent "<script>alert(10*2*3);</script>"
    # from getting an <em> tag inserted in the middle
    markup <- paste(sep = "\n",
      "This is *emphasized* text in markdown.",
      htmlPreserve("<script>alert(10*2*3);</script>"),
      "Here is some more *emphasized text*."
    )
    extracted <- extractPreserveChunks(markup)
    markup <- extracted$value
    # Just think of this next line as Markdown processing
    output <- gsub("\\*(.*?)\\*", "<em>\\1</em>", markup)
    output <- restorePreserveChunks(output, extracted$chunks)
    output

[Package htmltools version 0.5.1.1 Index]