HTML closing tags are weirdly escaped in plotly json

When using plotly.R to produce json of a plot containing HTML, e.g. a bold tag, the closing tag's slash gets weirdly escaped, producing malformed HTML. (Somehow the Plotly FE still manages to render the HTML.) Python's plotly does not do the same escaping.

Note the "values": ["<b>A<\/b>", "<b>B<\/b>"]" below - I'd expect "values": ["<b>A</b>", "<b>B</b>"] instead.

> library(plotly)
> fig <- plot_ly(
  type = 'table', 
  header = list(values = c("<b>A</b>", "<b>B</b>") ),
  cells = list(values = rbind(1,1)))
> plotly_json(fig, jsonedit = FALSE)
{
  "visdat": {
    "70ec6031022f": ["function () ", "plotlyVisDat"]
  },
  "cur_data": "70ec6031022f",
  "attrs": {
    "70ec6031022f": {
      "header": {
        "values": ["<b>A<\/b>", "<b>B<\/b>"]
      },
      "cells": {
        "values": [
          [1],
          [1]
        ]
      },
      "alpha_stroke": 1,
      "sizes": [10, 100],
      "spans": [1, 20],
      "type": "table"
    }
  },
  "layout": {
    "margin": {
      "b": 40,
      "l": 60,
      "t": 25,
      "r": 10
    },
    "hovermode": "closest",
    "showlegend": false
  },
  "source": "A",
  "config": {
    "showSendToCloud": false
  },
  "data": [
    {
      "header": {
        "values": ["<b>A<\/b>", "<b>B<\/b>"]
      },
      "cells": {
        "values": [
          [1],
          [1]
        ]
      },
      "type": "table",
      "frame": null
    }
  ],
  "highlight": {
    "on": "plotly_click",
    "persistent": false,
    "dynamic": false,
    "selectize": false,
    "opacityDim": 0.2,
    "selected": {
      "opacity": 1
    },
    "debounce": 0
  },
  "shinyEvents": ["plotly_hover", "plotly_click", "plotly_selected", "plotly_relayout", "plotly_brushed", "plotly_brushing", "plotly_clickannotation", "plotly_doubleclick", "plotly_deselect", "plotly_afterplot", "plotly_sunburstclick"],
  "base_url": "https://plot.ly"
} 

compared to python - note the "values":["<b>A</b>","<b>B</b>":

>>> import plotly
>>> import plotly.graph_objects as go
>>> fig = go.Figure(data=[go.Table(header=dict(values=['<b>A</b>', '<b>B</b>']), cells=dict(values=[[1], [1]]))])
>>> plotly.io.to_json(fig)
'{"data":[{"cells":{"values":[[1],[1]]},"header":{"values":["<b>A</b>","<b>B</b>"]},"type":"table"}],"layout":{"template":{"data":{"histogram2dcontour":[{"type":"histogram2dcontour","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"choropleth":[{"type":"choropleth","colorbar":{"outlinewidth":0,"ticks":""}}],"histogram2d":[{"type":"histogram2d","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"heatmap":[{"type":"heatmap","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"heatmapgl":[{"type":"heatmapgl","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"contourcarpet":[{"type":"contourcarpet","colorbar":{"outlinewidth":0,"ticks":""}}],"contour":[{"type":"contour","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"surface":[{"type":"surface","colorbar":{"outlinewidth":0,"ticks":""},"colorscale":[[0.0,"#0d0887"],[0.1111111111111111,"#46039f"],[0.2222222222222222,"#7201a8"],[0.3333333333333333,"#9c179e"],[0.4444444444444444,"#bd3786"],[0.5555555555555556,"#d8576b"],[0.6666666666666666,"#ed7953"],[0.7777777777777778,"#fb9f3a"],[0.8888888888888888,"#fdca26"],[1.0,"#f0f921"]]}],"mesh3d":[{"type":"mesh3d","colorbar":{"outlinewidth":0,"ticks":""}}],"scatter":[{"fillpattern":{"fillmode":"overlay","size":10,"solidity":0.2},"type":"scatter"}],"parcoords":[{"type":"parcoords","line":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scatterpolargl":[{"type":"scatterpolargl","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"bar":[{"error_x":{"color":"#2a3f5f"},"error_y":{"color":"#2a3f5f"},"marker":{"line":{"color":"#E5ECF6","width":0.5},"pattern":{"fillmode":"overlay","size":10,"solidity":0.2}},"type":"bar"}],"scattergeo":[{"type":"scattergeo","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scatterpolar":[{"type":"scatterpolar","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"histogram":[{"marker":{"pattern":{"fillmode":"overlay","size":10,"solidity":0.2}},"type":"histogram"}],"scattergl":[{"type":"scattergl","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scatter3d":[{"type":"scatter3d","line":{"colorbar":{"outlinewidth":0,"ticks":""}},"marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scattermapbox":[{"type":"scattermapbox","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scatterternary":[{"type":"scatterternary","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"scattercarpet":[{"type":"scattercarpet","marker":{"colorbar":{"outlinewidth":0,"ticks":""}}}],"carpet":[{"aaxis":{"endlinecolor":"#2a3f5f","gridcolor":"white","linecolor":"white","minorgridcolor":"white","startlinecolor":"#2a3f5f"},"baxis":{"endlinecolor":"#2a3f5f","gridcolor":"white","linecolor":"white","minorgridcolor":"white","startlinecolor":"#2a3f5f"},"type":"carpet"}],"table":[{"cells":{"fill":{"color":"#EBF0F8"},"line":{"color":"white"}},"header":{"fill":{"color":"#C8D4E3"},"line":{"color":"white"}},"type":"table"}],"barpolar":[{"marker":{"line":{"color":"#E5ECF6","width":0.5},"pattern":{"fillmode":"overlay","size":10,"solidity":0.2}},"type":"barpolar"}],"pie":[{"automargin":true,"type":"pie"}]},"layout":{"autotypenumbers":"strict","colorway":["#636efa","#EF553B","#00cc96","#ab63fa","#FFA15A","#19d3f3","#FF6692","#B6E880","#FF97FF","#FECB52"],"font":{"color":"#2a3f5f"},"hovermode":"closest","hoverlabel":{"align":"left"},"paper_bgcolor":"white","plot_bgcolor":"#E5ECF6","polar":{"bgcolor":"#E5ECF6","angularaxis":{"gridcolor":"white","linecolor":"white","ticks":""},"radialaxis":{"gridcolor":"white","linecolor":"white","ticks":""}},"ternary":{"bgcolor":"#E5ECF6","aaxis":{"gridcolor":"white","linecolor":"white"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>>> 

Start at plotly_json(fig, jsonedit = FALSE) and reproduce the table example with bold HTML values, comparing the emitted R JSON with the shown Python output. Trace the JSON serialization path and verify the closing tags are emitted as rather than </b>; done means the R output preserves the expected HTML while remaining valid JSON.