#include "bits/stdc++.h"


#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep1(i, n) for (int i = 1; i < (n); ++i)
#define rep1n(i, n) for (int i = 1; i <= (n); ++i)
#define repr(i, n) for (int i = (n) - 1; i >= 0; --i)
#define pb push_back
#define eb emplace_back
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define each(x, a) for (auto &x : a)
#define ar array
#define vec vector
#define range(i, n) rep(i, n)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using str = string;
using pi = pair<int, int>;
using pl = pair<ll, ll>;

using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pair<int, int>>;
using vvi = vector<vi>;

int Bit(int mask, int b) { return (mask >> b) & 1; }

template<class T>
bool ckmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool ckmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

// [l, r)
template<typename T, typename F>
T FindFirstTrue(T l, T r, const F &predicat) {
    --l;
    while (r - l > 1) {
        T mid = l + (r - l) / 2;
        if (predicat(mid)) {
            r = mid;
        } else {
            l = mid;
        }
    }
    return r;
}


template<typename T, typename F>
T FindLastFalse(T l, T r, const F &predicat) {
    return FindFirstTrue(l, r, predicat) - 1;
}

const int INFi = 2e9;
const ll INF = 2e18;

void solve() {
    int n, m;
    cin >> n >> m;
    vector<vi> a(n, vi(m));
    rep(i, n) {
        string s;
        cin >> s;
        rep(j, m) {
            a[i][j] = (s[j] == 'B');
        }
    }
    rep(t, 2) {
        auto b = a;
        vector<string> res;

        int x, y;
        string cur;
        auto Go = [&] (int x2, int y2) {
            assert(x2 >= x && y2 >= y);
            while (x < x2) {
                cur.push_back('D');
                x++;
                b[x][y] ^= 1;
            }
            while (y < y2) {
                cur.push_back('R');
                y++;
                b[x][y] ^= 1;
            }
        };
        if (min(n, m) >= 2) {
            // i - j == c
            // (0, m - 1) -> -(m-1)
            // (n - 2, 1) -> n-3
            for (int c = -(m - 1); c <= n - 3; ++c) {
                // [0, n - 2]
                x = 0;
                y = 0;
                b[x][y] ^= 1;
                cur.clear();
                for(int i = 0; i <= n - 2; ++i) {
                    int j = i - c;
                    if (1 <= j && j < m && b[i][j] != t) {
                        Go(i, j);
                    }
                }
                Go(n - 1, m - 1);
                res.push_back(cur);
            }
        }
        if (b[0][0] != t) {
            x = 0;
            y = 0;
            cur.clear();
            b[x][y] ^= 1;
            Go(n - 1, m - 1);
            res.push_back(cur);
        }
        assert(res.size() <= 400);
        bool ok = true;
        rep(i, n) {
            rep(j, m) {
                ok &= (b[i][j] == t);
            }
        }
        if (!ok) continue;
        cout << "YES\n";
        cout << res.size() << '\n';
        rep(i, res.size()) cout << res[i] << '\n';
        return;
    }
    cout << "NO\n";
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(12) << fixed;
    int t = 1;
    cin >> t;
    rep(i, t) {
        solve();
    }
    return 0;
}